Brain Bee Flashcards
What are the brain’s three layers of protection?
Bones, meninges and ventricles
What are the two bones that protect the CNS?
Cranium and vertebrae
What is the durable outermost layer of the meninges?
The Dura Mater
What is the thin, delicate, 2nd layer of the meninges?
The Arachnoid Mater
What are the Pia Mater and Arachnoid Mater collectively known as?
The Leptomeninges
What is the space between the Dura Mater and Arachnoid Mater known as?
The subdural space
What is the thin, innermost layer of the meninges that adheres directly to the brain, going deep into its grooves?
The Pia Mater
What is the important area between the arachnoid mater and pia mater that is filled with blood vessels and fine tissue projections known as?
subarachnoid space
What are the fine tissue projections that connect the dura mater and arachnoid mater, and circulate CSF known as?
trabeculae
What are neurons/nerve cells in charge of?
Transmitting and integrating information in the brain.
What are dendrites?
Branched extensions of a nerve cell that receive inputs from other neurons
What is the cell body/soma?
A part of a neuron that contains the nucleus and other organelles. It is where all the dendrites converge and their electrical inputs are combined.
What are axons?
A single (often long) process which branches to form terminals that contact other neurons and/or cells.
What are terminals?
The endings of the axon through which many neurons signal information to the next cell, generally using chemical neurotransmitters.
What cells make up gray matter?
Neurons
What cells make up white matter?
Glial cells
What do glial cells do?
Maintain an optimal environment for neuronal function, by protecting neutrons, providing structural support,, scavenging debris, managing waste and supplying them with nutrients.
What types of glia are found in the CNS?
Astrocytes, microglia, oligodendrocytes and ependymal cells
What types of glia are found in the PNS?
Schwann cells and satellite cells
What do astrocytes do?
Deliver nutrients from the blood to neurons and take waste products.
Control the chemical environment, like ions and transmitters, around neurons and other brain cells (the “extracellular environment” or “microenvironment”) to keep them healthy and regulate metabolism.
Responsible for controlling capillary blood flow, which in turn modulates the flow of chemicals between blood and neurons.
Astrocytes play an important role in repair and scarring of nerve cells in the CNS
Astrocytes provide a buffer reserve of “fuel” for cells as they contain glycogen (a large molecule made of glucose sub-unit molecules) which they can break down to release glucose during periods of high demand by neurons.
They also regulate excess K+ homeostasis.
What do oligodendrocytes and Schwann cells do?
Provide a myelin sheath to insulate the axon of neurons, allowing faster connections. They also provide trophic support to neurons through secretion of neurotrophic factors.
Contribute towards maintaining an optimal extracellular environment
What are microglia?
Specialized immune cells that make up the main active immune defense mechanism in the CNS.
A particluar type of macrophage (special white blood cells) only present in the CNS.
What do microglia do?
They scavenge cell debris from dying neurons and other glial cells and are the “first responders” when there is damage to the CNS. The scavenging actions of microglia can prevents the build up of toxic waste substances but may also contribute to neurodegeneration.
They constantly and rapidly reorganize their shape by changing their processesdue signalling from K+ channel signals, this allows them to very efficiently scan the local environment to identify any insults to the CNS. their cell body doesn’t change shape, so that it doesn’t disturb local neuronal circuits.
Microglia play important roles in regulating the development of the brain after birth, and in brain plasticity in adulthood.
What do ependymal cells do?
Line the brain’s fluid spaces (ventricles) to form a slight barrier between the fluid spaces and the cells, while producing CSF.
Ependymal cells have cilia, little hair-like organelles that face the cavity of the ventricles. The cilia time their movement to direct CSF and are can influence the distribution of neurotransmitters to neurons.
Some ependymal cells can divide and form neurons through the life of a cell, allowing neuroregeneration to occur.
These support cells can provide an environment that protects axon stumps from degeneration after damage, allowing alternate neuronal connections to grow and restore function.
What do satellite cells do?
Found only in the ganglion of the PNS, they regulate the external microenvironment and respond to neuronal injuries.
What do trophic molecules do?
Aid in the growth and development of other molecules.
What do tropic hormones do?
Stimulate glands to make other hormones.
How many axons can one neuron have?
1
What is the most diverse and common glial cells in the NS?
Astrocytes
Where are protoplasmic cells found?
In the gray matter
Where are fibrous cells found?
In the white matter
What is the Blood Brain Barrier made of?
A network of tightly packed endothelial cells
What do astrocytes do? (summary)
Neurogenesis (growth + development of nerve tissue
Synaptogenesis (formation of synapses between neurons
Immune Response
Glial Scars
Blood-Brain Barrier
Maintain Homeostasis
Vasomodulation (the neuronal regulation of blood flow)
What are the 2 division of the NS?
The Central Nervous Systema and Peripheral Nervous System
Where are nerves in the CNS located?
In the brain and spinal cord
Where are nerves in the PNS located?
Outside the brain and spinal cord
What are the 2 divisions of the PNS?
The autonomic NS
The somatic NS
Where are neurons in the ANS located?
In deep internal structures (the gut, the heart, the lungs, the blood vessels…)
Where are neurons in the SNS located?
More superficially located structures (the skeletal muscles of the body, the eye, the ear…)
What are afferent neurons?
Neurons that run from the periphery (the body) to the CNS, carrying information to the CNS.
What are efferent neurons?
neurons running from the CNS to the periphery, carrying information to body parts (the periphery)
What groups are neurons in the CNS located in?
Structures called nuclei or fields
What groups are neurons in the PNS located in?
Structures called ganglia
What are bundles of nerve axons called?
Nerve Tracts (or fasciculus)
What makes white matter white?
The presence of a fatty substance called myelin
What do sequences of nucleus to tracts to nucleus to tracts… create?
Neuronal circuits
What do sequences of nucleus to tracts to nucleus to tracts… create?
Neuronal circuits
What does the SNS control?
Voluntary functions
What does the CNS control?
Involuntary functions
What does the Enteric NS control?
The gastrointestinal tract
what does the ANS control?
.Involuntary functions
What are motor efferent neurons?
Neurons that transmit information from the CNS to control muscles.
What are sensory afferent neurons?
Neurons that transmit information from sensory organs to the CNS.
What are the 2 types of interneurons?
Local Neurons
Projection (tract) interneurons
What are the 2 types of interneurons?
Local Neurons
Projection (tract) interneurons
Where are interneurons located?
Only in the CNS
What do interneurons do?
Transmit information from one neuron to the next neuron.
What do interneurons do?
Transmit information from one neuron to the next neuron.
What distance do local neurons transmit over?
Short distances between neurons within the one nucleus)
What distance do local neurons transmit over?
Short distances between neurons within the one nucleus)
What distance do projection neurons transmit over?
Long distances (between neurons located in two different nuclei)
What do neuroendocrine cells do?
Receive neural input and release hormones into the blood supply to influence distant target organs.
What do unipolar neurons have?
A single process and no dendrites
What is the principal type of sensory neuron in the NS?
Pseudo-unipolar cells
What do the soma of pseudo-unipolar neurons make up?
Sensory ganglia in the PNS
What are bipolar neurons?
Neurons with two extensions: one axon, and one dendrite, that are mostly sensory neurons
What are multipolar neurons:
Neurons with one axon and numerous dendrites
What does an axon extend from?
The soma
What region of neurons is the axon
The conducting region
What insulates myelinated axons
A myelin sheath
What is region is the axon hillock/initial segment?
The integration region
What is region is the axon hillock/initial segment?
The integration region
What is region is the axon hillock/initial segment?
The integration region
What is region of neurons is the axon hillock/initial segment?
The integration region
What does the integration region do?
It collects all the information that a neuron receives before determining if there is sufficient excitation to relay that excitatory information along the conducting region.
What does a cells cytoskeleton consist of?
Micro-filaments and neuro-filaments for rigidity, and microtubules for transport
Where are axon terminals located on a neuron?
Specialized regions called synapses
What region of neurons are synapses
The output region
What region of neurons are synapses
The output region
What region of neurons are synapses
The output region
What do dendrites receive?
Synapses/inputs
What are the small protrusions on dendrites called?
Dendritic spines
What occurs at dendritic spines?
Excitatory inputs are provided by other neurons, they are the region through which chemicals flow into the cell when it is activated.
What protein allows dendrites to change shape (elongate and contract)?
Actin
What are the 3 classification of dendritic spines?
Thin
Mushroom
Stubby
What are thin dendritic spines known as?
Learning spines: they have been shown to grow when a new task is being learned.
What are mushroom dendritic spines known as?
Memory spines they are formed from the thin spines when learned tasks are remembered.
At different stages of life, as well as in different disease states, different proportions and density of ___ are observed?
Dendritic spines
Alcoholism is associated with a ____ in dendritic spine density.
decrease
With learning, dendritic spine density ___
increases
What are microtubules used for in neurons?
Transport of nutrients and waste products and the chemical neurotransmitters used to transmit information from the neuron’s terminals to the next cell/s in the chain. (Packages of nutrients or wastes are carried like along a conveyor belt along the outside of the microtubule.)
The accumulation of organelles and particles in one area of a neuron results in ___
swelling of the axon and eventually in disconnection and lesioning of the axon (axotomy) - leading to neuronal death.
What are the myelin sheaths of axons formed by (myelinated fibres)?
Schwann cells (in PNS) or oligodendrocytes (in CNS).
In myelinated axons, the glial cell wraps itself around a part of the axon and winds itself tighter and tighter by ___
squeezing all its own content out to the outermost winding, so that all the inner windings of the sheath consist only of the cell membrane of the glial cell.
What insulates some axons?
Myelin sheath
What do myelin sheathes prevent that results in a speeding up of flow of information?
Leakage of current
What do neurons do at their synapses?
contacts other cells to relay information or commands. (It is the function output region of a neuron)
What is the gap that separates cells called?
A synaptic cleft
How wide is a synaptic cleft?
approx. 20nm (nanometers)
What do neurons use to carry information across the synaptic cleft?
chemical neurotransmitters
What is the presynaptic neuron?
The signalling neuron
What is the postsynaptic neuron?
The target cell
When information is being sent from neuron to cell, what regions are sending and receiving the information?
The pre-synaptic neurons terminals to the post-synaptic neurons receptors
What do micro- and neuro- filaments provide?
A framework for structural rigidity.
What does the input region include
The soma and dendrites
What are the CNS and PNS connected to each other by?
Afferent and efferent neurons
What is the CNS?
The control center that processes all the information it receives from sensory neurons about the environment, and decides whether it should make a response or do nothing.
What are the planes of section?
The horizontal plane
The coronal plane
The sagittal plane
In the brain, what is the center referred to as?
The midline
What are structures close to the brain’s midline called?
Medial
What are structures far from the brain’s midline called?
Lateral
What are structures on both sides of the brain’s midline called?
Bilateral
What axis describes how close something is to the spinal cord/brain
The proximal-distal axis
In the proximal-distal axis, what are hands and feet considered?
Distal
In the proximal-distal axis, what is the trunk considered?
Proximal
What is the axis that describes whether something is to the front or back of the body?
The anterior-posterior axis
What axis describes whether something is to the top to the bottom?
The superior-inferior axis
What axis describes whether something is towards the belly or back?
The ventral-dorsal axis
What axis describes whether something is towards the head or tail?
The rostral-caudal axis
What is the spinal cord?
A long tubelike structure found inside the vertebrae, that is connected to the end of the brain stem.
What is the main function of the spinal cord?
To connect the brain to the nerves of the PNS; it is the main pathway for the brain to send information to the periphery
What are the 5 regions of the spinal cord?
The cervical region The thoracic region The lumbar region The sacral region The coccyggal nerve
How many pairs of spinal nerves are there?
31
What is the hole in the center of the spinal cord?
The central canal
What is the central canal filled with
CSF (which helps in nourishing the nerves tissue and acts as a shock absorber)
What is in a spinal nerve?
Nerve tracts (fascicles) and blood vessels
What is the membrane surrounding the spinal nerve called?
The epineurium
What is the membrane surrounding a nerve tract/fascicle called?
The perineurium
What do fascicles/nerve tracts cotain?
Many neurons
What is the membrane surrounding a neuron in the spinal nerve called?
The endoneurium
What is the dorsal root of a spinal nerve for?
Sensory afferent neurons
What is the ventral root of the spinal cord for?
Motor efferent neurons
What are the 3 main regions of the brain?
The brainstem
The cerebellum
The cerebrum
How many pairs of cranial nerves are there?
12
What arteries supply the brain with blood?
The internal carotid artery
The vertebral artery
What do the two vertebral arteries join to form?
A single basilar artery
Where do the two vertebral arteries join?
on the ventral surface of the hindbrain.
What does the basilar artery divide to form?
The two posterior cerebral arteries
Where does the basilar artery divide?
Near the front end of the pons
What does the internal carotid artery form?
the anterior and middle cerebral arteries.
What is the oldest part of the brain?
The brainstem
What is the brainstem involved in?
Involuntary body functions (functions that you do not control through conscious thinking.)
What does the brainstem continue from?
The spinal cord
Where does the brain stem join the forebrain?
At the top end (rostral end)
What are the 2 main parts of the brainstem?
The hindbrain and midbrain
What is the rostral part of the hindbrain?
The pons
What is the caudal part of the hindbrain?
The medulla oblongata
How many neuromeres/segments is the midbrain made of?
2
How many neuromeres/segments is the hindbrain made of?
12
What is the hindbrain segment closest to the midbrain called?
the isthmus
What are the neuromeres of the hindbrain called
the isthmus
rhombomeres (r1 to r11).
What is the cerebellum involved in?
control of fine-movements
What does the cerebellum grow out of?
The rostral hindbrain
What part of the brain is above the pons?
The midbrain
Where are axons from the midbrain sent to?
The cerebellum, to modulate the activity of neurons in higher centers of the brain in the context of functions like sleep, attention or reward.
What are the two small “hillocks” of neurons in the Midbrain?
The colliculi
What are colliculi involved in?
Relaying auditory information or in automatic reflex responses where we move our heads and/or eyes to a sudden unexpected sound or object or touch.
What are the brainstem contains centers (collections of nuclei) that send pathways to keep the forebrain awake and alert called?
The Ascending Arousal System (AAS)
What is a corridor through which pathways (tracts) travel from forebrain to cerebellum and spinal cord, and from spinal cord to forebrain.
The brainstem
The brain stem is connected to motor neurons and sensory receptors by what?
ten pairs of cranial nerves: Cranial Nerves III - XI
Where does the oculomotor (III) cranial nerve arise from?
The midbrain
Where do cranial nerves IV-XI arise from (there is 9 of them)?
the hindbrain
What do the large myelinated tracts in the brain stem include?
descending tracts from the cerebral hemisphere, ascending tracts carrying sensory information to the thalamus, and the cerebellar input and output systems
How much of the brain’s volume does the cerebellum take up?
10%
How much of the brains neurons are in the cerebellum
Over half
What skills does the cerebellum control?
Coordination, balance, posture, and movement.
How much of the brain’s volume does the cerebrum take up?
83%
Just above the midbrain and between it and the cerebrum lies what part of the brain?
The Diencephalon
The Diencephalon consists of structures lying on either side of what?
the fluid-filled third ventricle.
What are the ventricles?
a set of four interconnected fluid-filled cavities in the brain, part of the protective elements of the CNS.
What are the names of the 4 ventricles?
right and left lateral ventricles (the first and second ventricles)
third ventricle
fourth ventricle
Which ventricle is continuous with the central canal of the spinal cord.
The 4th ventricle
What do the ventricles produce and contain?
CSF: which bathes and cushions the brain and spinal cord.
What are the collection of nuclei in the diencephalon called?
The thalamus
The hypothalamus
(it also contains the epithalamus and the sub-thalamus.)
Where must information be sent before it arrives at the cortex in the cerebrum
The thalamus
What separates the different thalamic subparts?
A system of myelinated fibres
Where is the thalamus in the brain?
It is a midline symmetrical structure within the brain situated between the cerebral cortex and midbrain.
The thalamus relays sensory and motor signals to where?
The cerebral cortex
Thalamic nuclei have strong reciprocal connections (to-and-fro connections) with the cerebral cortex that are believed to be involved with what?
consciousness.
What does the thalamus play a major role in?
regulating arousal, awareness level, and activity.
Where is the hypothalamus?
An almond-sized structure just below the thalamus, is a mass of nuclei in such close proximity to each other, they look like a single structure anatomically
What does the hypothalamus perform?
Vital functions (e.g., regulation of certain metabolic processes), most of which relate directly or indirectly to the regulation of activities involving internal organs.
What does the hypothalamus perform must of its functions via?
hormones that it releases or whose release from the pituitary gland it controls, and
nerve connections to other brain regions to control the ANS that controls internal body activities
what are the prominent nuclei within the hypothalamus?
the suprachiasmatic, paraventricular, ventromedial, and mammillary nuclei.
hypothalamic outputs can be divided into what?
neural projections and endocrine hormones.
What body functions do the hypothalamus control?
Body temperature, hunger, thirst, fatigue, sleep, complex homeostatic functions and circadian cycles.
The hypothalamus produces and secretes a wide variety of neurohormones that lead to what?
the release or inhibition of hormones from the pituitary gland below the hypothalamus.
The hypothalamus produces and secretes a wide variety of neurohormones that lead to what?
the release or inhibition of hormones from the pituitary gland below the hypothalamus.
What does the pituitary stalk connect the hypothalamus to?
the pituitary gland
What are the 2 parts of the pituitary gland?
the anterior and posterior pituitary.
Through what does the hypothalamus pass signals back and forth between the anterior and posterior pituitary?
the neurohypophysis and median eminence.
What is the posterior pituitary is made up of?
tissue derived from the hypothalamus
what is the anterior pituitary is derived from?
epithelial tissue.
What are hormones produced in the hypothalamus secreted by?
The pituitary gland
the anterior pituitary produces its own hormones under the control of what?
releasing factors (hormones) produced in the hypothalamus
The hypothalamic endocrine control is located where?
in the paraventricular nucleus which secretes the releasing hormones.
What does the SCN sits on top of?
the optic chiasm at the base of the brain
What does the SCN also receives direct input from to synchronize the clock with day and night.
the retina
What does the subthalamus connect to?
the globus pallidus
what is the globus pallidus?
a basal nucleus of the telencephalon.
Where does the subthalamus receive afferent connections from?
the substantia nigra and striatum
What does the subthalamus regulate?
skeletal muscle movement
The epithalamus functions as a connection between what?
the limbic system and other parts of the brain.
Some functions of the epithalamus include:
the secretion of melatonin by the pineal gland (involved in circadian rhythms) and regulation of motor pathways and emotions.
Where is the epithalamus located?
it is a dorsal posterior segment of the diencephalon, that is also connected to the limbic system and basal ganglia.
Where is the pineal gland located?
In the epithalamus
What is the main function of the epithalamus
Secretion of melatonin by the pineal gland
What is another name for the cerebrum of the brain?
The telencephalon
What can the cerebrum be divided into
A left and right hemisphere
What is the left hemisphere more involved in?
logical thinking
What is the right hemisphere more involved in?
creative activities
What are the two hemispheres of the cerebrum connected by?
3 nerve tracts
What is the most prominent nerve tract connecting the hemispheres of the cerebrum called?
The corpus callosum
What is the outer covering of gray-mater in the cerebrum called?
the cortex
What structures does the cerebrum contain?
the hippocampus, amygdala, olfactory bulb, and basal ganglia.
what is the innermost layer of the cerebrum?
the basal ganglia
what are the basal ganglia?
collections of subcortical nuclei in each hemisphere that help regulate voluntary movements
What activities does the cortex play a role in?
Consciousness, thinking, personality, memory, learning, attention, language, perception and movement.
What activities does the cortex play a role in?
Consciousness, thinking, personality, memory, learning, attention, language, perception and movement.
What activities does the cortex play a role in?
Consciousness, thinking, personality, memory, learning, attention, language, perception and movement.
What is the back block of the cerebrum?
The sensory block: it processes sensory information leading to a conscious awareness of the world around us.
How much of the cerebrum does the sensory block take up?
60%
What is the middle block of the cerebrum?
The motor block: it controls directed and planned movements, including overcoming obstacles in the way.
How much of the cerebrum does the motor block take up?
20%
What is the front block of the cerebrum?
The executive block: controls our executive functions, which determine our personality, consciousness and thinking.
How much of the cerebrum does the executive block take up?
20%
What are the ridges of the cortex called?
Gyri
What are the shallow grooves of the cortex called?
Sulci
What are the deep grooves of the cortex called?
fissures
what separates the cortex into the two hemispheres?
longitudinal fissure
what divides each hemisphere into lobes?
Deep sulci
What are the lobes of the brain?
the frontal lobe
the parietal lobe
the temporal lobe
the occipital lobe
How many cortical layers are there?
6
What happens in the upper layers of the cortex?
information is integrated, and where different forms of learning occur.
What happens in the middle layers of the cortex?
these are the input layers, receiving information from the lower regions of the brain.
What happens in the inner layers of the cortex?
Axons are sent to other brain regions.
What are the sub-cortical structures of the cerebrum?
the hippocampus, amygdala, olfactory bulb, and basal ganglia.
Where is the amygdala located?
In the temporal lobe rostral to the hippocampus, with one amygdala in each half of the brain in the left and right temporal lobes.
What is the amygdala involved in?
Complex behavioural and emotional responses - related to fear, to social organisation, in evaluating the emotionality of situations, and for learning based on reward or punishment.
It helps us recognise potential threats and then works through the ANS to help prepare us for fight-or-flight reactions, it causes an increase in heart and breathing rate.
What is the limbic system?
A connected set of structures that includes parts of the thalamus, hypothalamus, hippocampus, the amygdala and olfactory bulb.
What is the amygdala part of?
The limbic system
What does the limbic system (including the amygdala) regulate?
Emotions and behaviours related to fear and motivation.
Memory formation and consolidation, especially emotionally important memories. This is done together with the hippocampus, which is adjacent to the amygdala.
What are the major basal ganglia nuclei that control movement?
the striatum and the globus pallidus, both located deep in the cerebrum.
What are the main parts of the striatium?
The caudate and putamen
The basal ganglia works with a structure called the ___, in the midbrain, to coordinate and make smooth a sequence of behaviours to achieve a target desired outcome movement
substantia nigra
The globus pallidus is a layered nucleus that lies where?
just medial to the putamen
The hippocampus is found where?
Under the cerebral cortex, in the medial temporal lobe
What is the hippocampus involved in?
How information is moved from short-term memory to long-term memory and consolidated there,
and in spatial memory that enables navigation
Has a role in the formation of new memories about experienced events (episodic or autobiographical memory The proximity of the hippocampus to the amygdala, which is involved in emotions, allows for easy interactions between them and may explain the way that emotion is often tied up to memories of specific episodes.
The hippocampus, including the dentate gyrus has what shape?
A curved tube
The hippocampus is a well-established area for the study of what?
the phenomena of long-term potentiation (LTP) and long-term depression (LTD) in the transfer of information between neurons, phenomena that are believed to play a role as the neural substrate of memory.
Why is it difficult to find and treat neurodegenerative diseases?
Because brain functions involve widely-distributed areas that are all interconnected, it is difficult to uniquely pinpoint a specific brain region as being responsible for a particular functional problem.
It also makes it difficult to treat disorders - when we target an area to treat a disease or disorder, we don’t know what the upstream (higher-up) or downstream (lower-down) effects might be.
What are the 3 main factors that contribute to the aging of the brain?
Oxidative stress
Immune Dysfunction
Impaired protein recycling
What is the main region of the brain affected by neurodegenerative diseases?
The cortex
What is neural signaling?
When neurons receive input or commands, and then transmit this information along their length, relay the information or command to the next neuron in the series.
What are the two ways for neurons to do neural signaling
Through the flow of current (electrical signalling)
Through the flow of chemicals (chemical signalling)
What is a cell that is being relayed information by a neuron called?
A target cell
What do neutrons have a different of across the cell membrane?
electrical charge
Is the inside or outside of a neuron more negative?
The inside
Is the difference of electrical charge of a neuron across the membrane or on either side of the cell membrane alone?
Across the cell membrane
What is the difference in charge across the cell membrane?
-70mV
Why is a neurons membrane polarized?
Because across the cell membrane there is a difference in electrical charge
What is the difference in electrical potential known as?
The Resting Membrane Potential (EM or RMP)
What is it called when the RMP becomes less negative than the resting value?
de-polarized
What is it called when the RMP becomes more negative than the resting value?
hyper-polarized
Where are separations in charge across the membrane found?
many cells, as well as intra-cellular membrane-bounded organelles such as mitochondria, peroxisomes, and lysosomes.
In mitochondria, the importance of the loss of the separation in charge across its membrane results in what?
the failure of the chain of molecules used to produce the energy molecule, ATP. Ending the useful life of that mitochondrion.
What do neurons use when they carry information along their length?
current flow (electrical signaling)
What do neurons use to relay information to the next neuron in a series?
chemical flow (chemical signaling)
In biological systems, what is charge carried by?
Ions
The difference in charge across the cell membrane must be due to differences in the movement of ___ across the membrane.
ions
In neurons, the RMP is due to that, at rest, the nerve allows ___ to move across the cell membrane more easily than they allow ___ to move across.
- potassium (K+) ions
2. sodium (Na+) ions
what do neurons use to maintain the movement of ions across the two sides of the cell membrane (to maintain a constant RMP)
An ‘active pump’
What does ‘active’ mean in a biological system?
That it requires energy to conduct activity
If the function of this pump were inhibited, what would occur?
the balance of ions would not be maintained and then the RMP would be lost
In neurons, what will failure to maintain the RMP result in?
failure of the neuron to signal information, possibly resulting in harm or death to person.
In neurons, what will failure to maintain the RMP result in?
failure of the neuron to signal information, possibly resulting in harm or death to person.
If a neuron wants to signal that it has received an input, what must it do?
change the RMP, by changing the flow of ions, resulting in a current flow across the neutrons length
What are ions?
Charged particles, with an excess or deficit of electrons relative to protons
As the current flows along a neutron, it leaks out and so has to be recharged, how is this done?
By producing an action potential
What is an action potential
a large change in the membrane potential; a change that is so large that it provides a reservoir of “new energy” to power the information further along the neuron.
What is an action potential
a large change in the membrane potential; a change that is so large that it provides a reservoir of “new energy” to power the information further along the neuron.
It is a series of changes that occur in the RMP when the neuron receives an input
In the Action Potential, the resting membrane potential
goes from a rest value of -70mV all the way to +30/+40mV, then back down to -90mV, then back to rest (-70mV)
How long does an AP go for?
Very brief- 2 milliseconds long
What is the rapid series of changes in the resting membrane potential called?
the Action Potential (AP; or nerve impulse or nerve spike).
This change occurs at a very localized point along the neuron and as it occurs, the current is already flowing to where?
adjacent parts of the neuron; to produce an AP at those points.
What happens when the current is flowing to adjacent parts of the neuron; to produce an AP at those points?
Information is spread away from the site which first triggered the AP
What is current?
The movement or flow of an electrical charge
Why is the flow of information across a neuron quite a slow process?
Because an AP is generated at every adjacent point along the neuron
What are the two ways that the flow of information can be sped up?
Increasing the diameter of the neuron
Insulating the neuron with a myelin sheath
These both reduce the number of AP points, speeding up the flow of information
What is the gap between neurons sometimes bridged by so neurons only have to use electrical signaling?
special channels
Why can’t electrical signaling be used to transfer information across the gaps between the neurons?
Because the current/ions would be washed away in the fluid found between cells
Why is there an unbridged gap between neurons that requires chemical signaling?
Because usually, you don’t want commands from one cell to instantaneously produce a response in the target cell. You want the target cell to get a number of different commands or inputs which it can then balance off, to “decide” whether to respond.
What are the 2 general types of chemical signaling?
synaptic signaling
non-synaptic signaling
what is the synaptic cleft?
A gap across which a neuron contacts a target cell
What is synaptic signaling used by?
only by neurons
What is non-synaptic signaling used by?
neurons and non-neuronal cells
In synaptic signaling what chemical agents are used?
neurotransmitters
What distance is involved in synaptic signaling?
short distances
What chemical agents are used in non-synaptic signaling?
Hormonal and local chemical mediators
What local chemical mediators are used in synaptic signaling?
Paracrine and autocrine
What distance is non-synaptic signaling using hormonal chemical chemical agents involved in?
long and very long distances
What distance is is non-synaptic signaling using paracrine local chemical mediators involved in?
short (adjacent cells)
What distance is is non-synaptic signaling using autocrine local chemical mediators involved in?
very short (on to self)
The use of chemicals is a ___ for signaling information in the body.
ubiquitous (found everywhere) mechanism
What does chemical signaling require?
Chemical signals released by a cell.
A cell with specialized structures called receptors, to bind the chemicals and produce a response.
What chemicals are generally used to transmit information for short periods of time, with (generally, but not always) short-lasting effects.
Water-soluble chemicals
What chemicals tend to be hormones with long-lasting effects, e.g., in growth and development, in hormonal cycles like the menstrual cycle etc.
Lipid-soluble chemicals
What types of chemical signaling are water-soluble chemicals found in?
Synaptic and non-synaptic signaling (both neurons and non-neuronal cells)
What types of chemical signaling are lipid-soluble chemicals found in?
Non-synaptic signaling (non-neuronal cells only)
what are the specialized structures on target cells for chemicals to bind to on the target cell called?
receptors
what are the specialized structures on target cells for chemicals to bind to on the target cell called?
receptors
What is the location of a receptor related to?
the type of chemical they bind
what chemicals cannot penetrate the cell membrane of the target cell.
Water-soluble chemicals
where are receptors for Water-soluble chemicals located?
in the membrane of the target cell and facing the world outside the cell.
What chemicals are membrane-bound
water soluble chemicals
what type of chemicals can penetrate the cell membrane?
Lipid-soluble chemicals
Where are receptors for Lipid-soluble chemicals located?
inside the cell, or on the cell surface
What type of chemicals are intracellular
Lipid-soluble chemicals
What are the types of receptors for water soluble chemicals?
receptors that form ion channels
receptors linked to G-proteins
receptors linked to tyrosine kinase
What are receptors?
specialized structures on cells that chemicals bind to in order to elicit an effect.
All receptors have a particular structural region that can bind chemical signals, what is it called?
the binding site
What is the normal chemical that binds to a binding site called?
A ligand or agonist
Only a part of the ligand – not the whole ligand - binds to the binding site. So two chemicals with ___ can fit into the binding site and bind to the receptor
similar structures
Why can drugs and medications bind to a binding site?
they have a similar structure to the ligand
When drugs and medications bind to binding site they either:
elicit similar response to the agonist (acts as the agonist)
or
blocks the binding site without eliciting a response itself but preventing the natural ligand from eliciting a response (act as an antagonist).
The effects of the ligand are to bind to the appropriate receptor(s) and cause a ___ in the receptor.
shape change
when a ligand binds to a binding site, what leads to the cellular response in the target cell?
the shape change in the receptor
what are the two types of receptors?
Membrane-bound receptors
Intra-cellular receptors
In some receptors the binding of the ligand to the binding site doesn’t itself affect the movement of ions across the membrane instead:
the binding of the ligand changes the shape of the receptor on the inside of the target cell.
The change allows a molecule found in the cell to bind to the receptor, resulting in responses in the target cell.
Usually ___ are used to produce slower, but long-lasting, changes in the target cell because the ___ leads to actions on the cell’s DNA.
Since DNA is the genetic material of the cell, affecting the DNA will alter the way proteins and other molecules are produced, leading to long-term changes.
- intracellular receptors
2. receptor-ligand interaction
What is the affect of membrane-bound receptors that form ion channels?
The voltage changes directly
What is the affect of membrane-bound receptors linked to G-proteins?
. The voltage changes indirectly through the G-proteins or 2nd messengers
. Cellular changes indirectly through 2nd messenger which act on biochemical and genetic (DNA) processes.
What is the affect of membrane-bound receptors linked to Tyrosine kinase?
Alters biochemical function to affect cell function
What is the affect of intracellular receptors that bind to DNA?
Alters biochemical function to affect cell function
Extracellular signal causes ___ which causes conformational change which causes ___
- Binding to receptors
2. Cellular response
In membrane bound receptors, binding of the ligand to the receptor site will change what?
the movement of ions across the membrane
Different regulatory sites can change what?
how ligands elicit responses
What is the binding site for in a NDMA type glutamate receptor?
glutamate
What is the binding site for in a NDMA type glutamate receptor?
glutamate
What are the regulatory sites for in a NDMA type glutamate receptor?
Glycine, zinc, PCP, and Mg2+
What is the regulatory site for a Kainate type glutamate receptor
zinc
What is the NDMA type glutamate receptor critically involved in?
learning and memory
What is the Kainate type glutamate receptor critically involved in?
Everyday transmission of information between neurons
What is the Kainate type glutamate receptor critically involved in?
Everyday transmission of information between neurons
What is the chemical GABA (Gamma-amino-butyric acid)
An inhibitory transmitter
What is an inhibitory transmitter?
A receptor hat it reduces the likelihood of the target cell responding. It is a major way the brain can prevent a cell from responding when not needed.
What two regulatory agents enhance the inhibitory affect of GABA?
benzodiazepines (BZDs) and barbiturates
Agents that bind to regulatory sites on GABA receptors on their own will ___ GABA receptors, but binding all together at the same time will cause the channel pore to open even wider and cause ___ of the cell
- Bind and activate
2. Major suppression
Each sensory system has ___ to cope with a different type of ___
- evolved
2. stimulus
all sensory systems have to:
convert the physical energy of some stimulus to which they are specialized into a biological response.
Action potentials occur in ___ that will therefore carry the information about the ___ to the brain for ___ , and many other things.
- nerve fibres
- stimulus
- interpretation and learning
conversion of physical stimulus energy to biological energy, leads to:
the production of action potentials, or changes in the timing and number of action potentials.
Our senses are not just windows to the external world but also the drivers of much of our ___
internal world of thoughts, feelings, desires and memories.
The eye is specialized to tell us about:
the features of visual objects through detection of electromagnetic radiation emanating from them.
The ear is specialized to detect:
the pressure waves that make up sound.
Our tongues and our noses are specialized to detect:
the food-borne or air-borne chemicals in what we taste or smell.
what two steps do all sensory systems do?
Convert the physical energy of an appropriate stimulus into a biologically meaningful form.
Encode that information in the form of APs in nerve cells that carry that information to the brain as a train of APs.
In the brain there are great similarities between the way in which the ___ for each sense ___ the information they receive from their specific ___.
- specialized brain areas
- process
- sensory peripheral elements
Our senses detect only a ___ of the ___ in a ___.
- small amount
- energy
- stimulus domain
In every species, each ___ responds only to a ___ in that domain of stimuli
- sensory modality
2. specific range of stimuli
The range of a stimulus energy possessed by an animal is related to what?
the evolutionary niche occupied by the animal.
what is Johannes Muller’s Law of specific nerve energies?
the nature of perception is defined by the pathway over which the sensory information is carried.
In every sensory system we will find specialized cells, ___, that contain mechanisms and processes that allow them to ___ to only ___ type of ___.
- receptors
- respond
- one
- physical stimulus
What do systems detecting the state of things in external undertake? and what are their receptors called?
Exteroception
Exteroceptors/Extero-receptors
What are systems detecting the relationship of our body to the world (position and movement of limbs & body in space) called? and what are their receptors called?
Proprioception
Proprio-receptors / Proprioceptors
What are systems that detect the state of things within the body are undertaking? What are their receptors called?
Interoception
Intero-receptors/Interoceptors
What are sensory systems that respond to stretch or deformation are undertaking? What are their receptors? Examples: Hearing, Balance, Blood pressure, Muscle stretch, Gut filling, Proprioceptors.
Mechano-reception
Mechano-receptors
What are sensory systems that respond to light are undertaking? what are their receptors? – Example: Vision.
Photoreception
Photoreceptors
What are sensory systems that respond to chemicals are undertaking? What are their receptors? – Example: Taste, Smell, Blood gases, Osmoreceptors (that monitor fluid composition).
Chemo-reception
Chemo-receptors
What are sensory systems that respond to changes in temperature are undertaking? What are their receptors? Example: Somatosensation (sensations from our body, both outside and inside).
Thermo-reception
Thermo-receptors
What are sensory systems that respond to painful / damaging stimuli are undertaking? and what are their receptors? Example: Somatosensation (sensations from our body, both outside and inside).
Noci-reception/Nociception
Noci-receptors/Nociceptors
Where do APs occur?
Nerve fibres
What are examples of peripheral components?
The eye, the ear, the skin
What are examples of central components?
The brain, the spinal cord
What do peripheral components do?
convert the physical energy of a stimulus into a biological form for transmission to the spinal cord and brain (central components).
The brain interprets sensory inputs to give us:
a sense of the world, influencing learning and cognition and for evoking and linking to memories.
All sensory systems have to get ___ efficiently to the region where they can be ___ into a biological response.
- stimulus energy
2. decoded
All sensory systems have to have ___ that convert the stimulus energy to a ___. All sensory systems have to have structures to convey the information from the biological response to the ___ where it can be interpreted or new things learnt, or memories formed.
- specialized structures
- biological response
- brain
What are the 3 parts of the Peripheral Sensory System?
Accessory structures Receptor Cells Output Neurons (afferent nerve fibres)
What do accessory structures do?
Detect stimulus energy, translate stimulus to receptor cells (translation)
What do receptor cells do?
Perform the receptor/generator potential- transduce stimulus to a biological response (transduction)
What do output neurons do?
Convert receptor potential to APs- transmit information to the CNS (transmission)
What are the 3 stages of the Peripheral Sensory System:
translation
transduction
transmission
What are the 3 stages of the Peripheral Sensory System:
translation
transduction
transmission
What are the two components of all senses?
Central and peripheral
Accessory structures translate ___ to receptor cells
stimulus energy
Receptor cells transduce ___ as a biological response
generator potential
Output neurones such as afferent nerve fibres transmit information to the Central Nervous System in the form of ___
action potentials
The biological response in all sensory systems to their appropriate stimuli is an ___ one - a change in the electrical of the ___. This can occur because ___ have a ___
- electrical
- biological response
- receptor cells
- RMP
when a stimulus directly acts on the cell membrane of the receptor, what occurs?
ion channels are opened or closed.
the ___ acts on a ___ to produce a ___ in the form of a change in the ___.
- stimulus
- receptor cell
- biological response
- biological resting charge difference
in indirect receptor ion channels, the stimulus acts on the ___ of the receptor to activate a ___, the ___ of which acts on ___ to cause them to open or close. This will modulate the ___ compared to the ___, and thereby change the ___ between the inside and outside compared to the resting electrical charge difference between the inside and outside.
- cell membrane
- cascade of molecules
- last
- ion channels
- movement of ions
- rest state
- electrical charge difference
What sensory systems act directly on the receptor ion channels?
Mechanoreceptors
What sensory systems act indirectly on the receptor ion channels?
chemoreceptors, photoreceptors, thermoreceptors, nociceptors.
Are receptor cells more or less polarized than neurons?
less polarized
Receptor cells are ___ with a ___ through them even when there are absent stimuli.
- leaky cells
2. “standing current flow”
What is the process when a stimulus directly affects receptor ion channels?
stimulus; receptor cells; structural change in membrane; opening or closing of ion channels; conductance change (altered movement of ions); change in RMP
What is the process when a stimulus indirectly affects receptor ion channels?
stimulus; receptor cells; structural change in membrane; activated molecules; opening or closing of ion channels; conductance change (altered movement of ions); change in RMP
What is conductance change?
the altered movement of ions
What is the type of biological response generated in all sensory systems to their appropriate stimuli?
Electrical
What does an indirect effect on receptor ion channels involve acting on the cell membrane to activate?
a cascade of molecules
In what senses is the receptor not actually a separate receptor cell, but the specialized ending of a nerve fibre?
In the Skin senses (the Somatosensory system) and in Smell
In the Skin senses (the Somatosensory system) and in Smell, how is a train of APs generated?
Stimulus triggers specialized ending of nerve fibre (receptor surface), here, the Receptor Potential triggers a sequence of APs in the neuron, and the train of APs are transmitted along the length of the neuron - ultimately reaching the terminals where a chemical transmitter will be used to relay that information to the next neuron in the series, to the appropriate brain area.
Stimulus; receptor potential; modulation of APs in sensory neuron
In Hearing, Taste and Balance, how is a train of APs generated?
The receptor is a separate cell from the nerve fibre carrying information away.
The Receptor Potential triggers the release of chemical transmitter from the receptor cell to the nerve cell.
There, the transmitter will ultimately trigger a sequence of APs in the neuron, and the train of APs will be transmitted along the length ultimately reaching the terminals where a chemical transmitter will be used to relay that information to the next neuron in the series, to the appropriate brain area.
Stimulus; receptor potential; modulation of transmitter release from receptor cell; modulation of APs in sensory neuron
In Vision, how is a train of APs generated?
The receptor is a separate cell from the nerve fibre carrying information away, interposed between these two is a relay cell. So the Receptor Potential needs to be triggered or modulated for the release of chemical transmitter from the receptor cell to the relay cell.
This in turn triggers or modulates the release of chemical transmitter from the relay cell to the nerve cell.
There, the transmitter will ultimately trigger a sequence of APs in the neuron, and the train of APs will be transmitted along the length ultimately reaching the terminals where a chemical transmitter will be used to relay that information to the next neuron in the series, to the appropriate brain area.
Stimulus; receptor potential; modulation of transmitter release from receptor cell; modulation of transmitter release from relay cell; modulation of APs in sensory neuron
The information about the stimulus that sensory nerve fibres carry to the brain is what?
A train of APs
What can be said about the size of APs
They are invariant (stay the same)
Sensory systems vary what to describe the features of the stimulus they are sending to the brain.
The rate and timing of APs in the train of APs
Variation in the rate and timing of APs going to the brain is then used to how?
to code/signal different aspects of the stimulus.
what features can AP trains carry about a stimulus?
Constant/intermittent
Texture
Strength/intensity
when the sensory neuron produces APs throughout the duration of the stimulus, what does it signal to the brain ?
that the stimulus has been applied for the entire time (is constant).
when the sensory neuron only produces APs whenever the intermittent stimulus has been presented, what can the brain be signaled?
That the stimulus has been applied intermittently or varyingly.
What texture do closely spaced APs carrying information about?
Fine surface
What texture do widely spaced APs carry information about?
A rough surface
How can the texture of a stimulus be determined by a train of APs?
The spacing of the APs in the train give information about the stimulus texture
As we increase the stimulus strength, what happens to the number of action potentials we record from the sensory neuron ?
It increases
When stimulus are closely-spaced, what is the intensity/strength of the stimulus?
Strong/high-intensity
When stimulus are widely-spaced, what is the intensity/strength of the stimulus?
weak/low-intensity
What is stimulus quality about?
it’s about that element that allows us to distinguish between different colours or different pitches of sound.
How can stimulus quality be transmitted to the brain?
through a nerve train of APs
How can stimulus quality be transmitted to the brain?
through a nerve train of APs
How can stimulus quality be distinguished? eg: pitch/frequency of sound
Because each individual receptor, that detects quality of a stimulus, and its nerve fibres won’t respond to that full range we hear, but only to some part of the range. The different pitches will activate different receptors (or different combinations of receptors) and different nerve fibres, allowing us to hear different sounds.
What does hearing form in humans and many other animals?
The basis of social communication
What does hearing form in humans and many other animals?
The basis of social communication
What does audition dominate in the brain?
Temporal processing and spatial processing
What can audition give us information about?
What something is (we can recognized auditory objects.
Where something is (we can localize objects based on auditory processing alone).
What is sound?
A wave of pressure travelling through an elastic medium (e.g., air, water) by mechanical disturbance (vibration) of the molecules of the medium.
How do sound waves begin?
First, a vibrating surface alternately causes compression and rarefaction of air molecules adjacent to the surface.
• In the regions of compression, the mechanical disturbance of air molecules causes a temporary increase in local pressure to above atmospheric pressure.
• Rarefaction causes a temporary decrease in local pressure below atmospheric pressure.
• Each individual molecule only moves a small distance before it bumps into a neighbour, which in turn bumps into another molecule.
• This creates a wave of compression and rarefaction (i.e., a wave of pressure changes) that, with time, travels away from the vibrating surface, through the process of compression and rarefaction of air molecules at more distant points away from the surface.
What is a wave of compression and rarifaction?
a wave of pressure changes
What does the mechanical disturbance of air molecules cause?
a temporary increase in local pressure to above atmospheric pressure.
What does rarefaction cause?
A temporary decrease in local pressure below atmospheric pressure.
What is compression?
When air molecules are drawn together
What is rarefaction?
When air molecules are drawn apart
Each individual molecule only moves a small distance, how does the sound wave continue?
it bumps into a neighbour, which in turn bumps into another molecule.
How does a wave of compression and rarefaction, with time, travel away from the vibrating surface?
through the process of compression and rarefaction of air molecules at more distant points away from the surface.
Does compression or rarefaction occur first?
Compression
What is a sound wave?
A variation in pressure with time
What does the speed of sound depend on?
the elasticity and the density of the medium in which the pressure changes are happening.
What is the speed of sound in air?
340m/s
What is the speed of sound in salt water?
approx. 1500m/s
Why does sound travel faster through denser mediums?
Because the particles are closer together in denser mediums, and so will collide much more quickly with each other, therefore the pressure wave will travel faster from the source of vibration.
What is frequency of sound?
Number of variations in pressure per second
What is the level or amplitude of sound?
The size of the pressure variations
What is frequency measured in?
Hertz (Hz) (pressure variation cycles / sec)
What kind of sound contains a low number of cyclical variations in pressure per second
low-frequency sound
What kind of sound contains a high number of cyclical variations in pressure per second
high frequency sound
In acoustic measurements, sound pressure or acoustic pressure is what?
the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure, caused by a sound wave.
In air, and water, what is sound measured in?
Microphone and hydrophone
What is the SI unit for pressure?
Pascal (Pa)
What measure of sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. What units is it in?
SPL (sound pressure level), measured in decibels (dB) above a standard reference level.
What is considered as the threshold for human hearing?
The standard reference sound pressure in air or other gases is 20 μPa, (at 1 kHz).
The exact range of frequencies and levels depends on what factors?
Age
Exposure to loud sounds
Whether you’ve taken certain ototoxic drugs
Trauma to your head
The exact range of frequencies and levels depends on what factors?
Age
Exposure to loud sounds
Whether you’ve taken certain ototoxic drugs
Trauma to your head
What is the sound wave frequency range for human hearing?
20Hz to 20kHz (20,000Hz)
What is the sound wave intensity range for human hearing?
level: 10dB (intensity/loudness)
Sound pressure level (SPL): 120 dB SPL
What is a pure tone?
A sound containing only one frequency of cyclical pressure variations, i.e., it is the simplest possible sound.
What is the main role of interneurons?
To do decide what to do and transfer the information from the sensory neurons to the motor neurons
State the electrical charge inside and outside of the neuron when an action potential is generated.
Positive inside and negative outside
what are complex sounds?
sounds that contain a complex pattern of pressure variations. A number of different pure tones can be combined to compose a complex sound.
How does the inner ear work in the opposite way to the combination of complex sounds?
it effectively decomposes a complex sound into the constituent simple sounds.
What puts back together auditory information to allow us to hear the sound as it is, and not as the individual components.
The brain
What are most sounds we hear?
Complex sounds: Combinations of simple tones of a range of different frequencies
The frequency content of a speech sound depends on what?
it depends on what needs to be said before and after that sound.
What is the phenomenon of co-articulation?
the way in which when you say a sound it depends on what other letters (sounds) occur before and after, because these letters influence the frequency content of the sound.
What are the 3 subsections of the human ear?
the external ear, middle ear & inner ear (cochlea).
What structures on the side of the head does the external ear consist of?
Pinna, tragus, concha
Where do the structures of the external ear lie?
Outside and around the ear canal (the external auditory canal)
What is the ear canal?
the tube that leads into the head and finishes at the eardrum (or tympanum).
Where does the middle ear start?
behind the tympanum (or eardrum), at the end of the ear canal.
What is the middle ear?
an air-filled cavity containing three ossicles called the malleus, incus and stapes and the Eustachian tube.
What is an ossicle?
A very small bone
What are the names of the 3 ossicles in the middle ear?
malleus, incus and stapes
Where does the Eustachian tube start and lead to?
it leads from the middle ear cavity down to the back of your mouth.
When you move your ear back and forth, what does the Eustachian tube do?
equalizes the air pressure on the two sides of the eardrum
What occurs when fluid and pus drains down the Eustachian tube?
Fluids accumulate in the middle ear
There is a feeling of fullness in your ears
Because of that fluid, the ossicles don’t move efficiently and everything sounds muffled as less energy from sounds is able to get to the inner ear.
What is another name for the inner ear?
The cochlea
What is the inner ear / cochlea?
a coiled fluid-filled tube, completely encased in bone except for 2 membrane-covered openings, the oval and round windows.
sound energy is ultimately converted into action potentials in the auditory nerve fibres by what part of the ear?
The cochlea
What carries the APs from the cochlea to the brain (carries information from the cochlea to the brain)?
Auditory nerve fibres
Where are the sensory receptor cells in the ear?
The cochlea
What are auditory receptor cells sensitive to?
movement
What is the path of sound energy from the world to the cochlea?
The world → External auditory canal → Tympanum → Malleus → Incus → Stapes → Cochlea
What is another name for the ear drum?
Tympanum
How are sound waves converted to movement?
The pressure waves of sound energy are converted into movement, when the pressure waves hit the eardrum and cause it to move back and forth as pressure increases and decreases in the sound wave.
This cyclical eardrum movement causes cyclical movement of the malleus, the first of the middle ear bones, which lies against the eardrum.
Movement of the malleus causes movement of the incus, which then causes movement of the last of these bones, the stapes.
Movement of the stapes against the oval window of the cochlea causes movement of the cochlear contents.
In the middle ear, how are the sound waves converted into movement?
The sound pressure waves cause rhythmic movement of the eardrum and then movement of the three middle ear bones in succession.
What does the external ear act as?
a funnel sounds into the ear canal and to modify sounds to help us localize them in elevation.
How does the external ear modify sound?
Because the external ear has a complex set of ridges and valleys, it also modifies how some sounds get into the ear canal, in a way that helps us identify whether a sound is in front of or behind us.
These modifications of sound waves are important for our ability to tell the elevation of a source of sound.
What happens when sound waves reach the middle ear?
they strike the tympanum, causing it to vibrate
What are the ossicles in the middle ear attached to?
The first of the ossicles, the malleus, is attached to the eardrum;
The second, the incus, is attached to the malleus; and
The third, the stapes, is attached to the incus.
Finally, the stapes is resting and held in place against the oval window membrane of the inner ear, so that as the stapes moves, it pushes into and out of that membrane and that causes movement of the contents of the inner ear.
What causes movement of the contents of the inner ear?
the stapes moving, pushing into and out of the oval window membrane, causing movement of the contents of the inner ear.
Why is the ear such a complicated system?
Because the inner ear is filled with fluid.
Why will the pressure waves directly striking the oval window mean that very little of that energy gets transmitted into the inner ear.
Because fluid molecules are harder to move than are the air molecules through which the sound pressure wave has been travelling.
Between the air in the external ear and the fluid in the inner ear, what is there?
an impedance mismatch
What is the most important role of the mammalian middle ear?
that it optimizes how air-borne sound energy is able to cause displacement of the fluids in the fluid-filled inner ear.
Is the impedance of cochlear fluid or air higher?
cochlear fluid
if sound waves were to directly strike the oval window, what would happen?
most sound would be reflected back from the inner ear.
How does the Middle ear match the impedance of air-borne sound energy to the fluid-filled cochlea?
by amplifying the sound energy so that now there is “more” force being applied against the oval window when the stapes moves it.
What is the small, pointy tip that the cochlea coils to called?
the apex
how many tubes does the cochlea contain?
three compartments winding together up the spiral coil
What, in the middle of the cochlea, runs all the way up the spiral coil?
the auditory nerve
What is the auditory nerve made of?
a number of nerve fibres that radiate out from the middle of the cochlea.
there is a row of what along the full length of the cochlea?
receptor cells
What does the Organ of Corti contain?
the receptor cells and the auditory nerve fibres carrying information to the brain.
What are the two types of receptor cells in the inner ear?
Inner hair cells
Outer hair cells
What do Hair cells possess that stick out from their tops?
fine ‘hairs’ called stereocilia
what is the difference in electrical charge between the inside and the outside of a hair cell, with the inside being negative relative to the outside?
-60mV
What do all receptor cells have, even when there is no stimulus?
a “standing” current flow; there are ions flowing into and out of the cells.
what allows hair cells in the inner ear to have a standing current flow?
The stereocilia, which contain ion channels (pores for ions to flow through), so that when they are open, ions flow through the cell.
What is the RMP of hair cells determined by?
the intrinsic properties of the membrane, the distribution of ions across the cell, and the standing current flow.
If we modulate the ion channels in the stereocilia, what will this modulate?
the flow of ions into the cell, modulating the current flow into the cell, and thereby altering the RMP.
If the change is positive and the cell depolarizes enough across a hair cell membrane, what will happen?
the change to RMP will alter the release of transmitter from the hair cells to nerve fibres.
how do we get stereocilia to open up, alter current flow, and get depolarization, to increase the release of transmitter to the nerve fibres?
We bend them back and forth.
This happens when sound energy causes displacement (movement) of the eardrum which leads to movement of the ossicles in sequence, and finally the stapes moves into and out of the oval window membrane pushing into and pulling out of the fluid in the cochlea.
with one half-cycle of the pressure change of a simple sound wave, as the pressure increases, what happens?
the eardrum moves in, the stapes also moves into the oval window.
This displaces the cochlear contents away from the oval window and towards the round window.
with one half-cycle of the pressure change of a simple sound wave, as the pressure increases, what happens?
the eardrum moves in, the stapes also moves into the oval window.
This displaces the cochlear contents away from the oval window and towards the round window.
with one half-cycle of the pressure change of a simple sound wave, as the pressure decreases, what happens?
the eardrum moves out, the stapes also moves out of the oval window.
This displaces the cochlear contents towards from the oval window and away from the round window.
What does the vibration of the cochlear contents spread to.
base to apex of the cochlea.
what also travels through the fluids of the cochlear compartments?
“travelling waves” of cochlear movement
as the travelling wave of displacement of the cochlear partition and cochlear fluids travels along the cochlear partition, what happens?
It increases in size from the cochlear base to the apex.
It then reaches a peak at some particular point and then rapidly ceases
What does the position of the peak of the cochlear fluid “travelling wave” depend on?
the frequency of the sound
Vibration of the cochlea partition at each point is most sensitive to a different frequency, why does this follow a systematic pattern?
because of the shape and mass of the structures of the middle compartment.
Where do high sound frequencies peak in the cochlear?
at the cochlear base
Where do low frequencies peak in the cochlear?
at the cochlear apex
in between the cochlear apex and the base there is a systematic grading of what?
frequency
he cochlea “decomposes” complex sounds into what?
their simple constituents.
Each spot on the ___ vibrates to a range of ___. It’s just more ___ to one specific frequency.
- cochlear partition
- tone frequencies
- sensitive
Each of the simpler constituents of a ___ cause ___ at one particular point along the cochlea, and that point varies with the ___ of that simple constituent.
- complex sound
- peak vibration
- frequency
Why is stereocilia movement back-and-forth?
because partition vibration is up-and-down:
Sound causes the cochlear partition to vibrate up and down. Vibration of the cochlear partition up and down moves all the contents of the cochlear partition up and down as well.
Because of the fact that some of the structures of the Organ of Corti (like the tectorial membrane resting above the hair cell stereocilia) are “hinged” at different points compared to other structures, this means there is going to be movement of the hair cell stereocilia back and forth.
Why is stereocilia movement back-and-forth?
because partition vibration is up-and-down:
Sound causes the cochlear partition to vibrate up and down. Vibration of the cochlear partition up and down moves all the contents of the cochlear partition up and down as well.
Because of the fact that some of the structures of the Organ of Corti (like the tectorial membrane resting above the hair cell stereocilia) are “hinged” at different points compared to other structures, this means there is going to be movement of the hair cell stereocilia back and forth.
What do cyclical movement of the stereocilia cause?
cyclical opening and closing of the ion channels.
Movement of ___ in one direction opens the channels, allowing ___ to flow into the cell.
Since K+ is ___, the cell is gaining positive charge.
This ___ the cell, i.e., makes less negative the negative ___, even to the point of making it positively charged inside the cell.
This depolarization spreads down the hair cell and, at the base of the hair cell, causes the release of ___ which is stored there in vesicles.
- stereocilia
- potassium ions (K+)
- positively charged
- depolarizes
- resting membrane potential
- transmitter
The transmitter of hair cells can bind to receptors on the ___ and lead to the production of ___ in the nerve fibres. The action potentials are ___ to the brain to inform it about sounds.
- nerve fibre
- action potentials
- transmitted
Vibration of the cochlea causes hair cells and then transmitters to do what?
become depolarized and release transmitters.
Transmitters then activate the nerve fibres attached to the appropriate hair cells.
What is the process of converting a physical stimulus to a biological response in hair cells?
vibration of partition; receptor potential in hair cells; APs in nerve fibres.
The further the frequency from the frequency to which a hair cell are most-sensitive:
the louder the sound has to be to activate the receptor.
Hair cells are most sensitive to one specific frequency so:
they require the least amount of sound intensity at that frequency to be activated
Why is there a pattern to frequency sensitivity in nerve cells?
vibration activates the hair cells which activates the nerve cells, therefore we should see the same pattern of sensitivity in nerve fibres depending on where they get their input from
what frequency are nerves on the cochlear base most sensitive to?
high frequency
what frequency are nerves on the cochlear apex most sensitive to?
low frequency
What does the frequency sensitivity of a nerve depend on?
where from the cochlea the nerve fibre is getting input
why can people lose sensitivity to some frequencies but not others?
Because if you were to damage the apex of the cochlea, or the receptors at the apex or the nerve fibres from the apex, you’d only lose hearing sensitivity to low frequency sounds.
Conversely, if you were to damage the base of the cochlea, or the receptors at or nerve fibres from the base, you’d lose hearing sensitivity to high frequency sounds.
Why do more people suffer damage to hearing of high frequencies?
Because the base of the cochlear is more easily damaged.
How much of our brain contains neurons devoted to processing visual information?
almost 30%
How does light produce a biological response?
stimulus; receptor cells; structural change in membrane; activated molecules; ion channels open/close; conductance change (altered movement of ions); change in RMP
What are receptor cells in the eye called?
photoreceptors
What do photoreceptors convert to a biological response?
electromagnetic radiation
How is physical stimulus converted to a biological response in the eye?
by using a chain of activated molecules between stimulus acting on the cell and the biological response in the cell.
What is the biological response in the photoreceptors communicated to?
intermediate relay cells (bipolar cells).
what do intermediate relay cells (bipolar cells) communicate the stimulus information to?
nerve fibres (retinal ganglion cells)
What are the step for getting the visual information from the externa world to the retinal ganglion cells?
Stimulus; accessory structures (sensory/receptive zone on the neuron); specialized sensory cell; intermediate relay cell; neuron (retinal ganglion cell)
Where is information from intermediate relays cells communicated to?
retinal ganglion cells
what is the outermost layer of the eye?
the Sclera – a tough connective tissue whose collagen layer continues forward to form the transparent cornea.
what is intermediate layer of the eye?
the choroid - a vascular layer that continues to form a lumpy structure called the ciliary body.
What does the choroid continue to form?
the ciliary body
What is the ciliary body composed of?
muscles, processes, and ligaments arranged in a ring, from which are attached the muscles of the Iris, around the lens
what is the innermost layer of the eye?
The Retina
what is the surface in the eye that holds photoreceptors?
The Retina
which structure is suspended behind the Iris by the lens ligaments coming down from the Ciliary Body.
the Lens
The posterior chamber behind the lens inside of the eye is filled with a jelly-like fluid, called what?
Vitreous Humor
The anterior chamber in front of the lens inside of the eye is filled with a watery fluid, called what?
the Aqueous Humor
What are the roles of the accessory structures in the eye?
Refraction & Accommodation
Regulation of light entry into the eye
Reduction of spherical aberration
What are all the structures in the eye before the retina?
accessory structures
As light rays travel from their source through the air they will be ___ (___ and bent from their original path of travel) at any interface where the rays encounter a change in the ___ of the ___ through which they are travelling.
- “refracted”
- slowed down
- density
- medium
When does refraction occur?
whenever the light rays encounter a medium with a different density – i.e., wherever there is a change in density, not in a medium with a uniform density.
what are the two common ways in which refraction occurs in spherical lenses?
convex lens
concave lens
Where does refraction occur in a lens?
at the front interface between the air and the lens and the back interface between the lens and the air.
When does refraction not occur?
When the medium is uniform
What type of lens causes divergence of light waves?
concave lens
Where is the focal point of a concave lens?
in front of the lens
Where is the focal point of a convex lens
behind the lens
What type of lens converges light rays?
A convex lens
Where are the three interfaces that experience refraction in the eye?
Air - cornea
Aqueous humor - lens
Lens- vitreous humor
What is the major site of refraction in the eye?
The air - cornea interface; it is the greatest density change
What type of lens is the lens in the eye?
a convex lens
the image that is formed at the back of the eye is ___. (Its’s our ___ that re-invert things so we don’t see the world like this)
- Upside-down
2. brain
When do common refractive errors of the eye occur?
when the amount of refraction from the accessory structures does not match the eyeball length.
Short-sightedness, or Myopia, is when:
the amount of refraction of distant light rays is too much for the eyeball length.
When the light rays from any distant point are brought to a focus in front of the retina and then diverge again, before striking the retina.
Thus, the light rays are not at a focus when they the hit the retina and therefore the image would be blurred
How is myopia corrected?
By using a concave lens force to force the light rays to diverge a bit prior to striking the eye.
What is another name for myopia?
short-sightedness
What is a cause of myopia?
When the eyeball is shorter than normal. This means the light rays will not yet be brought to a focus when they hit the retina, blurring the image
What is another name for hypermetropia
Long-sightedness
What is hypermetropia?
When the amount of refraction of distant light rays is not enough for the eyeball length.
Then, light rays from any one distant point are not sufficiently refracted to be brought to a focus on the retina.
Thus, the light rays are not yet at a focus when they the hit the retina, blurring the image.
How can hypermetropia be corrected?
we can force the light rays to converge a bit prior to striking the eye using a convex lens, in other words we can gain some extra refraction prior to the eye.
This extra refraction prior to the eye will now force the light rays, for the amount of refraction in the eye at rest, to be brought to a focus a little more in front of their previous focal point - i.e., on the retina rather than “behind” it.
What is astigmatism?
When the horizontal & vertical light rays from the same object get focused on different parts of the retina.
This arises because of corneal irregularities which make light rays from different planes (horizontal vs vertical) focus on different parts on the retina.
What is accommodation?
When the lens adjusts its curvature to allow us to see near objects occurs through a gain in the refractive power of the lens.
What does accommodation occur through?
the contraction of a set of ciliary muscles in the eye that control the tension on the lens, allowing it to become more curved (and thereby gain extra refractive power)
lens becomes more ___ → accommodation
spherical (fatter)
With age, accommodation ___ and plateaus after ___
- decreases
2. 50 years
- Explain how spectacle lenses are used to correct myopia
Myopia is when the refraction of distant light rays is too much for the eyeball length. Here, light waves from any one distant point are brought into focus in front of the retina and then diverge again before striking the retina.
A concave spectacle les will force the light rays to diverge slightly before striking the eye. This forces them, for the amount of refraction in the rest of the eye, to be brought to focus further back than before, providing the desired divergence to see clearly at distance.
What part of the eye regulates light entry?
the iris
Why does the iris increase or decrease to control the amount of light entering the eye?
- To prevent saturation of photoreceptors in bright light and allow maximum light capture in dim light.
- To reduce spherical aberration (which occurs with all lenses) - where the outer parts of the lens distort the image because of too much refraction.
What does the light regulation of the iris occur through?
the contraction of the muscles that make up the iris
Why do our lenses accommodate?
to see near object in sharp focus
Why do your pupils constrict?
to reduce light saturation from the near object and to reduce the spherical aberration distortion of the image
Why do your eyes converge?
so that both eyes are focusing on the same object
Automatic reflexes of light regulation in the eye are triggered by what?
the brain due to the defocusing (the “blurriness”) of the image as the object is closer, and these changes haven’t yet occurred.
What do photoreceptors do?
detect physical energy to produce a biological response.
What is the retina?
a highly layered structure of cells with the photoreceptors (called rods and cones) located at the back, furthest from the path of light.
Where on the retina are there no photoreceptors - so light rays falling on that region are not detected?
the blind spots
In species that hunt at night, there is often a ___ layer behind the ___, so that light rays which are not captured by the receptors in their first pass through the eye to the ___ can be reflected back for a second try at capturing them.
- reflective
- photoreceptors
- retina
What are rods for?
dim vision
How many types of rods are there?
1
how may types of cone cells are there?
3
What are cone cells for?
for daylight vision and allowing colour discrimination
What gives cones and rods their names?
the shape of the structure of the outer part of the receptors
What does the outer segment of photoreceptors contain?
the molecules that can absorb light energy.
What part of a photoreceptor connects the outer and inner segments?
the cilium
What does absorption of light energy set off?
a train of chemical reactions
The molecules involved in the cascade are found where in a photoreceptor?
the outer segment.
where are transmitter located to be released to relay cells?
the end of the inner segment
Where are intermediate relay cells found in relation to photoreceptors?
below the synapse of the photoreceptor
photoreceptors undertake ___ to relay information about ___ to the ___ in the series.
- chemical transmission
- light
- next cell
In photoreceptors, what 2 components does the visual pigment contain?
a chromophore and a protein opsin
What does a chromophore do in the visual pigment of photoreceptors?
absorbs light
when is a protein opsin activated?
when the chromophore absorbs electromagnetic energy.
what does a protein opsin hold in a particular way?
a chromophore
In both rods and cones, what is the chromophore (the light-absorbing molecule) called?
11-cis-retinal
What is 11-cis-retinal derived from?
vitamin A; that is why vitamin A deficiency can lead to certain forms of blindness.
What about the protein opsin differs between rods and cones, as well as between the different types of cones?
the structure of the protein Opsin that holds the chromophore in place for light absorption.
In rods, what is the visual called?
Rhodopsin
Cones use several types of cone visual pigments (all using 11-cis-retinal as the chromophore), differing only in the opsin type. What does this allow?
it allows each type of cone visual pigment to absorb light best at a different wavelength, forming the basis of our colour vision.
The receptors are distributed in ___ across the ___.
- specific ways
2. retina
Rods and cones are both absent at a spot at the back of the eye, what is this spot called?
The blind spot
___ are not ___ distributed across the retina.
- Rods and cones
2. uniformly
Where are cones highly concentrated?
the fovea (their numbers are very low elsewhere)
Rods are totally absent at the ___ - their numbers are greatest ___.
- fovea
2. beside the fovea
The numbers of cones ___ as you move to the edges of the eye but, except at the ___, they are always present at ___ than cones.
- decreases
- fovea
- much higher numbers
The brain ___ its guess of what we what should be in a ___
- “interpolates”
2. blind spot
- Outline why we don’t see blank spaces in our view:
When we look at the world, we don’t see blank spaces because our brain fills in that hole in our vision. It makes a guess based on what is around that blank hole in our vision, and based on our experience of the world, what might be a reasonable thing to continue across the blank hole. Therefore, the brain interpolates into the empty space in our vision so that people don’t have holes in their faces, or objects appear to be incomplete.
In rods the overall structure called Rhodopsin consists of what?
An opsin and 11-cis-retinal (chromophore)
The wavelength sensitivity of photoreceptors is due to what?
how the opsin holds the chromophore
The way in which the chromophore is held will determine what?
the wavelength of light it will absorb best.
There are 3 ___, each with their own ___ which allows each type of cone’s ___ to absorb light best at a different ___. This forms the basis of ___.
- cones
- opsin
- visual pigment
- wavelength
- colour vision
All ___ have the same ___, so they all show the ___
- rods
- opsin
- same wavelength sensitivity
What are the 3 colours of cones?
blue, green, red
what are metabotropic receptor?
G-protein coupled receptors (GPCRs).
Visual pigments are what type of receptors?
G protein coupled receptors (GPCRs) that come from a common superfamily of such metabotropic (G protein coupled) receptors.
when a GPCR is activated by an appropriate signal, what is it capable of?
binding and activating a G protein and that can set off a cascade of intracellular reactions.
In visual pigments the signal is what?
the energy in the electromagnetic radiations of light.
What is the binding site for the signal of energy in electromagnetic radiations of light?
he chromophore 11-cis-retinal
When a visual pigment is activated, what does it activate?
a G protein.
Once light activates the ___, then the activated visual pigment must activate ___. That in turn will activate a ___, the final one of which is a molecule that breaks down a molecule called ___.
- visual pigment
- a G protein.
- sequence of activations
- cyclic GMP
Light activates a molecular cascade that results in what?
the breakdown of a molecule called cyclic GMP into its non-cyclic form.
Breakdown of cGMP changes the flow of what?
Na+ and Ca2+ ions into the receptors.
A change in the flow of current from the ___ will produce the ___ in photoreceptors that signals the absorption of the ___.
- resting current flow
- electrical response
- stimulus light energy
Breaking down cyclic GMP produces what?
the biological electrical response.
Cylic GMP (cGMP) is actually like a ___—it holds open channels that allow the ___ into the cell.
- gate molecule
2. flow of sodium ions (Na+) and calcium (Ca2+) ions
When cGMP is broken down, it will prevent the flow of these ions into the receptors. This results in what?
A change in the flow of current compared to the resting flow.
In photoreceptors, the change in ___ from the resting state current flow will alter the ___ of the cell - it will change the ___
This produces a changed electrical state in ___ because they have absorbed the stimulus light energy.
- current flow
- resting membrane potential
- resting electrical state.
- photoreceptors
What are the steps for receptor cells signal the absorption of light stimulus energy?
light stimulus energy; activated rhodopsin; activated G-protein; activated enzyme (PDE); Cyclic GMP broken down to GMP; change in RMP of cell; signals biological response
What does the cascade system in photoreceptors allow?
amplification of the signal
Why does vision use a complex cascade system that requires 3 different molecules
because the cascade allows amplification of the signal.
A single photon of light can activate:
only 1 Rhodopsin molecule
Only 1 ___ is activated by a light stimulus, but in the ___, this can activate 10s
of the next molecule and each of those can activate 100s
of the next molecule and so on.
Thus the last molecule can alter the ___ of ___ of the cGMP molecule and that will affect the flow of a large amount of ___ into the cell.
- Rhodopsin molecule
- cascade of molecules
- cyclic status
- millions
- current
In a ___, a light ray has to activate the ___ and that has to activate the cascade, and the last molecule has to break down ___, and that has to result in a change in the ___, to change the resting electrical state, to signal the presence of ___.
- amplification cascade
- visual pigment
- cGMP
- normal (resting) current flow
- the stimulus
The amplification makes it much more likely that a single photon of light can result in what?
a significant enough biological response for all this to happen and for information to go to the brain.
A large change in the ___ makes it much more likely that there will be a ___ in the electrical properties of the ___, to be able to produce ___ to the next cell, eventually resulting in ___ in ___ that will carry that information to the brain.
- current flow
- sufficient change
- photoreceptor
- information flow
- action potentials
- nerve fibres
In signalling from a neuron to another cell, one mechanism involves ___ (GPCRs) which bind ___ to activate a ___.
The active G protein in turn activates secondary molecules, called ___.
This allows for ___ of the signal.
- metabotropic receptors
- transmitters
- G protein
- second messengers
- amplification
- Outline the steps of the amplification cascade and briefly explain why it is important:
A light ray has to activate the first visual pigment molecule, which activates a seconds molecule, and that third molecule finally acts on cyclic GMP (cGMP), the one which controls current flow in the receptor cell. cGMP changes the resting current flow, that in turn changes the resting electrical state to signal the presence of a stimulus.
Amplification results in a large change in the current flow, making it much more likely that there will be s a sufficient change in the electrical properties of the photoreceptor, to be able to produce information flow to the next cell, eventually resulting in APs in nerve fibres that will carry the information to the brain.
During daylight there is a lot of background bright light.
If light rays set off the cascade we described before, and break down cGMP to close off channels, why is it we can see anything at all in the daylight?
through light adaption
What does light adaptation allow?
it allows photoreceptors to cope with constant background (daylight) light.
In light adaption, the cell simply produces more ___ and does so faster, in ___ than in dark conditions.
By doing this, the ___ can continuously work against the break down of cGMP caused by the ___.
- cGMP
- bright daylight conditions
- photoreceptors
- background light.
As a bright light is kept on constantly, what happens to the electrical response in the photoreceptor?
the electrical response declines with time and the membrane potential returns to rest.
All sensory systems show a process of adaptation, what is this?
a decline in the response of the system even though the stimulus is maintained constantly.
What is the mechanism whereby we can allow our vision to operate in bright daylight?
Adaptation to a constant light stimulus,
The ___ has developed this compensatory mechanism (light adaption) whereas ___ hasn’t, despite the fact that our lives are surrounded by noise, most likely to do with ___.
Constant background annoying noise has really been with us only since the Industrial Revolution. Far too soon in our history for any___ - and evolution doesn’t work to create ___ to take care of environments that may exist in the future!
- visual system
- hearing
- evolution
- evolutionary compensation
- mechanisms
Does light adaption work better in cones or rods?
Light adaption works better in cones than rods
The process of light adaptation occurs in both ___ – i.e., both produce more ___ and do so faster, in ___ than in dark conditions.
- rods and cones
- cGMP
- bright daylight conditions
The light-induced breakdown of cGMP in rods is how much more efficient than in cones?
100 times more efficient
Even though ___ are producing more cGMP and doing so faster in bright daylight conditions, the efficient ___ causes cGMP breakdown as fast as cGMP is being produced.
Rods are not functional in signalling light from objects when there is ___ – during the day time.
Daytime vision is therefore dependent solely on ___.
- rods
- light absorption cascade
- bright background light
- cones
What type of receptors are foveal vision?
cones
What type of receptors are non-foveal vision?
rods
What is the difference between the direction of gaze of rods and cones? Why?
Cones are activated by axial gaze vs Rods universal gaze
Why: Location of receptors across retina: Cones are found almost only at the fovea so you have to look directly at an object to get cone vision into play (that’s why you need to look directly at an object to see it’s colour).
What is the difference between the colour detection of rods and cones? Why?
Cones are wavelength sensitive
Why: Type of protein opsins: Rods only have one type of opsin, cones have one of three different opsins, each of which absorbs light best at a different wavelength
What is the difference between the absolute sensitivity of cones and rods? Why?
Rods are more sensitive.
Why: Efficiency of cascade mechanisms: Rods have a more sensitive cascade that breaks down cGMP, so they are useful in very low light levels – e.g., at night. However, this sensitivity means they become non-functional when there is bright background light – sunlight.
What is the difference between the ability of rods and cones to signal fast events? Why?
Cones signal fast events, rods slow
Why: Recovery rate to rest: The responses in cones is less sensitive but faster recovering. So they can signal a second event occurring soon after the first. Rods are slow to recover to rest, so they are still responding to the first event when a second fast event occurs.
Information about what we see has to be transmitted to the brain by what?
retinal ganglion cells (RGCs)
What defines the photoreceptors that influence a retinal ganglion cell?
the receptive field of the RCG
each RGC only gets information from a ___ set of ___. This set makes up the ___ of that cell.
- finite
- photoreceptors
- Receptive Field (RF)
the region of the world from which light can act on photoreceptors to influence that specific retinal ganglion cell is what?
the receptive field of a RGCs
What are the parts of a RGCs RF?
The RF centre and the RF surround
How do the the receptors of the RF centre send information to a RCG?
via the direct pathway to the RGC
How do the receptors of the RF surround send information to a RCG?
via the indirect pathway to the RGC.
What are the two pathways of the concentric receptive field of a RGC?
There is a circular set of receptors that send information via the direct pathway to influence the train of APs that the RGC will send to the brain.
This is surrounded by another circle of receptors that send information via the indirect pathway to influence the train of APs that the RGC will send to the brain.
the size of the RF varies between RGCs according to what?
where they are located across the retina.
The RFs are smallest for RGCs getting information from the ___.
As you move away from the ___, RGCs getting input from receptors located away from the retina have ___.
- fovea of the retina
- fovea
- progressively larger RFs
What does it mean if a RF size is large?
.it means the RGC is getting input from a large circle of photoreceptors.
What does it mean if the RF size is small?
it means the RGC is getting input only from a small circle of photoreceptors.
What is acuity?
The ability to tell fine details
small RFs in the RGCs allow:
high visual acuity.
Each RGC is getting input from many photoreceptors which:
signal a different element of one stimulus or even from different stimuli.
RGCs with large RFs are summing up information across a:
large number of photoreceptors.
Large receptive fields can signal ___ at the expense of ___.
- the presence of an object/ detection of an object
2. poor visual acuity.
As RF size increases:
visual acuity should decrease, and therefore visual acuity should vary across the eye.
Where is day-time visual acuity the highest in the retina? Why?
the fovea
Why: because RGCs in the fovea have the smallest RFs
Cones are much less ___ than rods and the fovea contains only ___.
Thus when light levels are low, there isn’t enough ___ to activate cones and therefore the RGCs getting input from the cones will be silent.
However, even at night, ___ is highest in the region where functional RGCs have the ___ – now beside the fovea.
- sensitive
- cones
- light
- acuity
- smallest RFs
What part of the eye has the highest visual acuity at night?
The region beside the fovea (the para-fovea)
what photoreceptors does foveal vision have?
only cones
