Midterm #2 Flashcards
Basic division of human nervous system
- Central nervous system
–> Brain
–> Spinal cord - Peripheral nervous system
–> Somatic nervous system (skin, muscles and joints send signals to the spinal cord and brain), (Brain and spinal cord send signals to the muscles, joints, and skin)
–> Autonomic nervous syste, (Glands and internal organs send signals to the spinal cord and brain), (Brain and spinal cord send signals to the glands and internal organs –> further divided into sympathetic nervous system, and para-sympathetic nervous system).
Somatic Nervous System (SNS)
Transmits signals to CNS from muscles, joints, skin via nerves. CNS sends signals through SNS to muscles, joints and skin, to initiate, modulate, or inhibit movement.
Autonomous Nervous System (ANS)
Regulates internal environment of the body. Stimulates glands, and organs. Nerves of ANS project signals from these targets to CNS. Divided into sympathetic and parasympathetic system. They are opposing systems in terms of outcomes.
Sympathetic system
Signalling “fight or flight”; prepares body for action. Chronic stress leads to increased activity of this system.
Parasympathetic signalling
Signalling “rest and digest”; returns body to resting state.
Endocrine system
A communication network that influences thoughts, behaviours, actions. It works together with the nervous system. Signals slower than nervous system. Uses hormones to influence brain and body. Primarily controlled by hypothalamus, via signals to the pituitary gland.
Hypothalamus-pituitary-adrenal gland axis (stress response) in endocrine system
Hypothalamus secretes hormones corticotropin-releasing hormone (CRH) that stimulates pituitary to release adrenocorticotropic (ACHT), which increases cortisol production of the adrenal gland. Cortisol, on the other hand, inhibits production of CRH and ACHT, in a negative feedback loop.
Building blocks of Central Nervous System (CNS)
Neurons and Glial cells
Basic function of Neurons in CNS
Communication in form of propagating electrical signals
Basic function of Glial Cells in the CNS
Support and contribute to functions of neurons. There are microglia and there are macroglia.
Microglia glial cells
Protect CNS neurons. They are smaller than the other glial cells, and are mobile within the brian. They can metabolize dead tissue and are involved in keeping the CNS healthy.
Macroglia Glial cells
Astrocytes and oligodendrocytes are macroglia. Astrocytes link neurons to blood vessels, forming part of the blood-brain barrier, and they engulf synapses which regulate neurotransmitter release during synaptic transmission. Oligodendrocytes surround axons in the CNS, forming the myelin sheath that insulates axons, which allows the electrical signal that travels in the axons to travel faster.
Three basic types of neurons
- Multipolar interneurons (connect neurons with other neurons)
- Motor neuron (send information from CNS to the body’s effectors)
- Sensory neuron (act as receptors of stimuli, or are connected to receptors).
Anatomy of neurons
From cell body (soma), two kinds of cytoplasmic processes extend: a) one or more dendrites, and b) a single axon. Neurons can have different shapes, depending on their function and location.
Steps for information flow in the neuron
- A signal is received at the dendritic spines, at the post-synaptic terminals, where the neuron synapses with the axon of another neuron.
- This signal can produce an electric current that travels from the dendrite to the soma of the neuron.
- If the signal accumulating at the axon hillock in the soma is strong enough, the receiving neuron will “fire”.
- This electrical impulse travels down the axon toward the terminal buttons.
- When the electrical impulse reaches the pre-synaptic trminal, it can produce a chemical signal: the release of neurotransmitters.
- When neurotransmitters reach the post-synaptic terminal of the receving neuron: go back to point 1.
Electrical potential
Refers to how much energy is stored up in a system. When battery poles are connected in an electrical circuit, the potential can be released and converted for example in light energy.
The resting potential
At rest, when a neuron is not active, the electrical charge inside and outside the neuron is different. This difference in charge is called a potential. A neuron at rest has the resting potential of around -70 millivolts.
A brief change in the resting potential
If the electrical stimulation is strong enough, it exceeds the threshold of excitation and the axon of the stimulated neuron will fire an action potential. During the action potential, the neuron is briefly depolarized, so the membrane reaches about +40 mV.
Diffusion
Diffusion: refers to the phenomenon that particles tend to move from a region of high concentration to low concentration, eventually reaching an equilibrium of equal dispersion. Diffusion results from Brownian movement, which correlates with temperature. It is a force that pushes particles down their concentration gradient.
Electrostatic pressure
Refers to the fact that equally electrically charged particles repel each other, and differently charged particles attract each other. Applied to neurins: negatively charged molecules (anions), tend to move away from each other, and so do positively charged molecules (cations). Anions and cations are moving towards each other.
Ion channels in the neuron membrane
There are proteins in the neuronal membrane that form little channels, connecting the inside of the neurons with the outside. Some of these proteins allow certain types of ions to pass. These channels are called ion channels (example: sodium channels, potassium channels.) Some ion channels only open under certain conditions. These channels are called dependent ion channels.
Concentration of ions inside the neuron at rest
At rest, the concentration of negative ions inside the neuron is larger than outside, which has more positively charged particles than the inside. Unequal distribution of K+ and Na+ causes resting potential.
The resting potential: diffusion and electrostatic pressure
In the extracellular space (space outside neuron), we find a lot of NaCl in the solution, we also find K+. In the intracellular space (inside neuron), we find many negatively charged large proteins, K+, and about equal low amounts of Na+ and Cl-. As a consequence, during rest, the inside of the neuron has more negatively charged particles than the outside. This is why resting potential of neuron is negative.
Dynamics of diffusion and electrostatic pressure that determine resting potential.
Cl- is in greatest concentration outside, diffusion forces it inside. However, because there are many negatively charged organic anions inside, electrostatic pressure pushes Cl- out. K+ is higher concentrated inside, diffusion therefore pushes it out. However, the outside is positively charged, therefore at the same time electrostatic pressure pushes K+ in. Na+ is in greater concentration outside, so diffusion forces it inside. At the same time, electrostatic pressure pushes Na+ also inside. This is why there is the sodium potassium pump. Organic anions (negatively charged) cannot leave the neuron.
Ion flow during action potential
Resting potential at -70mV. Then an electrical stimulation exceeds threshold of excitation:
1. Sodium channels are voltage dependent channels: they open, and Na+ rushes into neuron (driven by force of diffusion and elecrostatic pressure.) this depolarizes the neuron membrane potential.
2. When depolarization reaches a point close to 0 mV, potassium channels open. K+ leaves neuron due to force of diffusion, and driven by electrostatic pressure from inside due to increase in positive charge from Na+ influx.
3. When depolarization reaches about +40mV, the sodium channels enter a refractory state and close: no more Na+ can enter the neuron.
4. The forces of diffusion and electrostatic pressure continue to force K+ out of the neuron. This reduces the positive charge inside the neuron, repolarising it.
5. When potential reaches resting potential, K+ channels close.
6. There is a slight hyperpolarisation, neuron reaches -70mV. Sodium-potassium pumps restore resting potential.
Release and Binding of Neurotransmitters
Neurotransmitter binding, depending on the transmitter and the receptor, can have a variety of outcomes. Some can hve an inhibitory effect (make it less likely that the post-synaptic neuron will fire). Some will have an excitatory effect (they make it more likely that the post-synaptic neuron will fire.
Control of Neurotransmitter Release
Synapse consists of: presynaptic terminal, synaptic cleft, post-synaptic terminal. It also includes glial cells that enclose three parts.
Three parts of synapse that glial cells enclose
Autoreceptor: senses the amount of released neurotransmitter to regulate exocytosis (release of neurotransmitters).
Reuptake: a reuptake mechanism “recycles” neurotransmitter from the synaptic cleft, moving it back into the presynaptic terminal. Some antidepressants interfere with this process for the neurotransmitter serotonin.
Enzymatic degradation: enzymes in the synaptic cleft degrade released neurotransmitters.
Summary of core events and concepts of signal transmission pt.1
When action-potential reaches the pre-synaptic terminal, it is converted from an electrical signal into a chemical signal. First, the action potential causes Ca2+ entry into the presynaptic terminal. This promotes that vesicles loaded with neurotransmitters (proteins) fuse with the presynaptic membrane. This causes neurotransmitter to be released into the synaptic cleft. There, they diffuse and eventually bind to receptors (proteins), that swim in the membrane of the post-synaptic cell.
Summary of core events and concepts of signal transmission pt.2
There are several different different types of receptors in the post-synaptic membrane of neurons in the CNS. Each receptor can bind a particular neurotransmitter. Binding the neurotransmitter can cause a specific action of the receptor. Now the chemical signal has been converted back into an electrical signal. This influx of electrically charged molecules can cause a depolarisation of the post-synaptic neuron, which can then lead to the neuron firing an action potential. Some neurotransmitters can have have the opposite outcome, they are inhibitory, not excitatory.
Summary of core events and concepts of signal transmission pt.3
Some receptors do not lead changes in charge when neurotransmitters bind to them, but they influence biochemical processes in the neuron, which can change the structure or functioning of the neuron. Released neurotransmitters are removed from the synapse by enzymatic degradation or reuptake into the presynaptic terminal. Some psychopharmacological drugs influence these processes.
Corpus Callosum
consists of millions of myelinated axons that connect the two hemispheres. Importance of this connection apparent in split brain patients.
Hemispheric organisation
Because the hemispheres are somewhat specialized, in split brain patients two independent forms of knowledge exist. Left hemisphere is critical for language: if split patient sees object with right eye, this is projected into the left hemisphere, and therefore the object can be named. What patient sees with left eye (projected to right hemisphere), cannot be named because right side does not have access to language system. However, patient can choose this item with the left hand (controlled by right side).
Frontal lobe principal functions
Cognition and memory. Ability to concentrate, judgement, consequence analysis, problem solve, plan, personality (including emotional traits)
Parietal Lobe principal functions
Plays an important role in integrating information from several senses. Also processes spatial orientation, some parts of speech, visual perception, and pain and touch sensations.
Occipital Lobe principal functions
Visual processing center of the brain. It contains most of what is referred to as the “visual cortex”. It is also the part of the brain where dreams originate.
Temporal Lobe principal functions
Chief auditory receptive area and contains the Hippocampus, which is the chief region where long-term memory is formed. Also deals with high-level visual processing (faces & scenes).
Brain Stem: Basic Survival Functions
Brain stem is the superior end of spinal cord. A main communication pathway between brain and body. Houses nerves that control basic functions. Reticular formation: projects into cerebral cortex, affects general alertness. Involved in sleep regulation.
Cerebellum
Essential for movement and proper motor function. For example, damage causes head tilt, balance problems. Essential for motor learning and motor memory. It operates independently. Cerebellum also involved in planning, event memory, language, emotions.
Thalamus: sensory relay
Is a gateway to cortex. With the exception of odour information, it receives all other sensory modalities. Smell, the oldest and most fundamental sense, has a direct route to cortex. During sleep, thalamus partially shuts down incoming sensory stimulation.
Hypothalamus
Hypothalamus is indispensable for survival. receives afferents from almost every body and brain region. Affects functions of many internal organs, regulates body temperature, blood pressure, blood glucose levels. Involved in motivated behaviours (thirst, hunger, aggression, lust.)
Basal ganglia
Critical for planning and producing movement. Afferents from entire cerebral cortex. Efferents to motor centres of brain stem. Damage can cause tremors and rigidity in Parkinsons’s disease, or loss of movement control in Huntington’s disease. Nucleus accumbens is part of basal ganglia, and is important for reward processing and motivating behaviour. This involves dopamine activity in the nucleus accumbens.
The Limbic System
Hippocampus essential for episodic and certain spatial memories. Hippocampus and amygdala densely connected. Amygdala processes emotions. Amygdala modulates processes in the hippocampus (and other brain regions), might signal importance of events, thus increasing their likelihood of being retained.
Psychophysics
Quantitative methods for measuring the relationship between physical and psychological events. Research aimed at relating physical stimuli to the contents of consciousness and behaviour.
Absolute threshold
The smallest stimulus level that can just be detected (and create a conscious experience)
Single detection theory
Accounts for individual biases
Just noticeable difference (JND)
The minimum difference that must exist between two stimuli before we can tell the difference them half of the time.
Sensation
The process by which our sensory organs detect a stimulus. We receive stimulus energies from different features of the environment.
Perception
Interpretation of sensory information to form a conscious representation of the stimulus.
Transduction
Transformation of one type of energy into another. It’s the conversion of stimulus energies from our environment into neural electrochemical energy (action potentials, neural signals).
Bottom-Up Processing
Also called data-based processing. Processing based on stimuli (elementary messages) in our environment.
Top-down Processing
Also called knowledge-based processing. Processing based on knowledge and memory to form a representation (perception).
Cornea
Transparent element of the eye through which light passes as it enters the eye.
Iris/Pupil
Coloured part of the eye. Muscular diaphragm that regulates entrance of light through contraction of the pupil (centre of iris).
Lens
Transparent element of the eye through which light passes after going through the cornea and aqueous humour (accommodation).
Retina
Surface on the back of the eye that contains a complex network of cells, including photoreceptor cells.
Fovea
Small area on the retina containing only colour-sensitive photoreceptors.
Optic nerve
Area of the retina where cells leave the eye and transmit action potentials to the brain. Creates a blind spot.
Photoreceptors
Responsible for the transduction of light into neural activity.
Cones
Respond better to bright light (daylight vision). Sensitive to specific wavelengths of visible light. Responsible for high-resolution (colour) vision. Around 5 million on the retina of each human eye.
3 types of cones
- S-Cones: Short-wave length cones (blues)
- M-Cones: Medium-wave length cones (yellow, greens)
- L-Cones: Long-wave length cones (orange, reds)
Rods
Respond better to dim light (nighttime vision). Sensitive to all wavelengths of visible light. Black and white vision. Very low resolution. Around 100 million rods in each human eye.
Location of photoreceptors on the retina
Rods are mostly found on the periphery. Cones are mostly found in the fovea.
Blind Spot
Where the optic nerve leaves the eye. There are no photoreceptors. The visual system usually fills in the blindspot with information from surrounding area.
Bipolar cells
Intermediate retinal neurons that receive input from the photoreceptors and send signals to retinal ganglion cells.
Diffuse bipolar cells
In the periphery. 1 diffuse bipolar cell responds to around 50 rods. Increased sensitivity but reduced acuity (50 rods; 1 diffuse bipolar)
Midget bipolar cells
In the fovea (centre). Receive input from a single cone and pass neural signal to a single ganglion cell (1cone: 1 midget bipolar).
Neural Convergence
Occurs when a number of neurons synapse onto a single neuron. Perception is shaped by neural convergence. Signals from rods converge more than signals from cones. Rods have better sensitivity than the cones, and cones have better acuity.
Ganglion cells
Retinal neurons that receive input from the retinal bipolar cells. Axons of ganglion cells leave the eye through the optic nerve.
M-Cell
Large ganglion cell. Mostly respond to rods via diffuse bipolar cells.
P-Cell
Small ganglion cell. Mostly respond to cones via midget bipolar cells.
A neuron’s receptive field
is the area on the receptor surface (retina) that, when stimulated, affects the firing of that neuron.
