The Nervous System Flashcards
How is the nervous system organised?
*CENTRAL NERVOUS SYSTEM (CNS)
brain and spinal cord
*PERIPHERAL NERVOUS SYSTEM
(Afferent neurons are those that take sensory information and direct it towards the central nervous system. Efferent neurons take messages from the CNS and deliver them to muscles and glands.)
-afferent neurons (sensory neurons)
-sensory input
-efferent neurons
somatic motor neurons (Somatic nervous system SNS)=voluntary actions and some reflexes.
OR
autonomic neurons (involuntary responses)
-sympathetic
-parasympathetic
(enteric nervous system)
There are neurons and glial cells
What do glial cells do?
They can keep balance of chemicals, maintain blood brain barrier, they make myelin (to make myelin sheath around axons )cerebral spinal fluid which is protective. They also have important immune function.
Describe the CNS
Brain
-2 major functions: control behaviour and to regulate the body’s physiological processes
-thought, forming memories, movement, and awareness
Spinal Cord
-Conducts signals to and from the brain
-Contains circuits of neurons which can control some of our simple reflexes
Cranial Nerves (16 of them)
-e.g. Optic nerve relay messages from your eyes to your brain to create visual images
Describe briefly what the cerebrum contains and does?
Cerebrum
*Hippocampus= Memory processing and retention
*Basal Ganglia= regulation of motor performance
*Amygdala: coordinate autonomic and endocrine responses of emotional states
*Cerebral Cortex (outer grey matter layer)= 2 hemispheres two halves are connected by a tube (they communicate by white matter tract called the corpus callosum)
Responsible for higher-order thinking, such as problem-solving, reasoning, and processing sensory information. It is divided into two hemispheres, the left and right, each controlling the opposite side of the body. The cerebrum can be further divided into four lobes:
What are Sulci, Gyri and fissure in the brain?
Sulci= fold/groove
Gyri=raised ridge
fissure=a deeper grove
The cerebrum consists of two cerebral hemispheres the outer layer called the cortex (gray matter) and the inner layer (white matter).
Describe the frontal lobe of the cerebral cortex
*Frontal Lobe: Involved in motor function, problem-solving, spontaneity, memory, language, initiation, judgment, impulse control, and social and sexual behavior.
Frontal lobe is divided into;
1. Primary Motor Cortex= Consciously aware of voluntary muscle movement. Brainspinal cordmuscle (middle of brain=higher extremities. Higher part of brain=lower extremities)
2. Motor Association Cortex=planning, processing and recognition of movement
3. Frontal Eye Field=voluntary eye movement
4. Prefrontal Cortex=Executive Functions, Behaviour, Personality
5. Broca’s Area=Typically located in the dominant hemisphere and stimulates the muscles that help us produce speech and form words
Describe the parietal lobe of the cerebral cortex
*Parietal Lobe: Responsible for processing sensory information it receives from the outside world, mainly relating to spatial sense and navigation (proprioception), the main sensory receptive area for the sense of touch.
Parietal lobe is divided into;
1. Primary Somatosensory Cortex=awareness of somatosensory, touch, pain and temp
Peripheralspinal cordbrain
2. Somatosensory Association Cortex=processing somatosensory, memory of sensation and compares to old, recognition of sensations.
3. Posterior Association Complex=Important for proprioception and Development of spatial awareness, it also extends into occipital and temporal lobes, Somatosensory stimuli – parietal lobe
Visual stimuli – occipital lobe
Auditory stimuli – temporal lobe
Describe the occipital lobe of the cerebral cortex
*Occipital Lobe: Primarily responsible for processing visual information.
The occipital lobe is divided into;
- Primary Visual Cortex=Awareness of visual stimuli
Eyeoptic nerveprimary visual cortexvisual association cortex - Visual Association Cortex=Processing visual info, understand, recognise, and use memory of stimuli
Describe the temporal lobe of the cerebral cortex
*Temporal Lobe: Involved in processing auditory information and is also important for the processing of semantics in both speech, vision and smell.
Temporal lobe is divided into;
1. Primary Auditory Cortex=Awareness of auditory stimuli
Earvestibulocochlear nerveprimary auditory cortexauditory association cortex
2. Auditory Association Cortex=processing, understand, recognise, memory of auditory stimuli
3. Wernicke’s Area= Usually in the dominant hemisphere. Comprehension and understanding of written and spoken language
4. Primary Olfactory Cortex/Associate Cortex=
Primary, consciously aware of smells
Association: Process, analyse, recognise
Describe the cerebellum
Cerebellum
Located at the back of the brain, it is responsible for coordination, balance, and fine muscle control. It contains Purkinje cells (neurons).
Describe all parts of the brainstem and what they do
Brain Stem:
1. Medulla oblongata
2. Pons
3. Midbrain
*The medulla contains the cardiac, respiratory, vomiting and vasomotor centres, and therefore deals with the autonomic functions of breathing, heart rate and blood pressure as well as the sleep–wake cycle
*pons handles all of your unconscious movements and processes. These cycles include everything from your sleeping to your breathing.
*The midbrain functions as a relay system, transmitting information necessary for vision and hearing. It also plays an important role in motor movement, pain, and the sleep/wake cycle.
Describe the diencephalon and what it’s divided into
diencephalon
It is involved in coordinating with the endocrine system to release hormones, relaying sensory and motor signals to the cerebral cortex, and regulating circadian rhythms
is made up of four main components.
1. Thalamus=Function: Sensory relay centre that directs sensory information to the cerebral cortex.
2. Subthalamus: Function: Primarily involved in motor control and coordination.
3. Hypothalamus: Function: Regulates homeostasis, controls the endocrine system, influences emotions and behaviours, and regulates the autonomic nervous system.
4. Epithalamus: Function: Contains the pineal gland, which produces melatonin, regulating the sleep-wake cycle and circadian rhythms. It also contributes to emotional responses and the sense of smell.
What is in the forebrain, midbrain and hindbrain
forebrain= cerebrum and diencephalon
midbrain=midbrain
hindbrain=pons, medulla oblongata and cerebellum
What is Proprioception?
Proprioception= co-ord of visual, auditory and somatosensory stimuli, spacial and body awareness
What are the meninges and what do the do?
They help with;
*Protecting the brain and spinal cord from physical injury.
Containing and circulating cerebrospinal fluid (CSF), which acts as a cushion and helps maintain a stable environment for the brain.
*Providing a barrier that helps prevent the entry of harmful substances and pathogens into the central nervous system.
*Supporting the blood vessels that supply nutrients to the brain and spinal cord.
The meninges are three protective layers that surround the brain and spinal cord:
*Dura Mater: Outer and tough.
*Arachnoid Mater: Delicate and holds cerebrospinal fluid.
*Pia Mater: Innermost, in direct contact with the brain and spinal cord.
They protect, cushion, and support the central nervous system. (even spinal cord)
What is the blood-brain barrier (BBB)?
The blood-brain barrier (BBB) is a protective barrier in the brain that separates the bloodstream from brain tissue. It prevents harmful substances from entering the brain, regulates the exchange of nutrients and waste, and maintains a stable brain environment. It acts as a defense against infections and can limit the effectiveness of certain drugs in reaching the brain.
What are spinal ganglia
Dorsal Root Ganglia contain the cell bodies of afferent nerve fibres.
Sensory impulses going to the CNS
Ventral Root Ganglia contain the cell bodies of efferent nerve fibres.
Motor impulses away from the CNS
What are the region that are vertebrae are divided into?
cervical nerves
thoracic nerves
lumber nerves
sacral nerves
coccyx
grey/white matter
in the brain the white matter is in the middle and grey is around the surface
In the spinal cord the white matter is outside and the grey matter is inside.
Ventricles & Cerebrospinal Fluid (CSF)
ventricles
*Open areas of the brain
*Make up the ventricular system
*Manufacture, circulate and reabsorb CSF
CSF
Plasma-like watery substance
Cushions and protects the brain and spinal cord
Allow the brain to ‘float’ in the cranium
Continuously circulates around these structures to remove impurities and deliver nutrients
“Flight or Fight” vs “Rest or Digest”
The autonomic nervous system is continuously producing responses – but essentially counteract or oppose one another
External stimuli can tip the scale in one direction or another
Sympathetic: generates physiological responses that occur from stressful or dangerous situations – FLIGHT OR FIGHT response
Parasympathetic: generates physiological responses when the body is at rest – REST AND DIGEST state
What could happen if the scales were tipped towards the sympathetic?
AND VICE VERSA
Critical actions for survival upregulated
-Tachycardia
-Cardiac Output
-Bronchodilation
-Mydriasis (pupil dilation)
-Hypertension
-Gluconeogenesis
-Diaphoresis (sweating)
Noncritical actions for survival downregulated
-Salivation
-Lacrimation
-Digestion
-Defecation
-Urination
Enteric Nervous System
Often gets grouped into the autonomic nervous system
However:
It is the independent intrinsic nervous system of the gastrointestinal tract
It has independent reflexes that do not rely on PNS
and sympathetic and parasympathetic signals can influence the enteric system
What are the two main nerve cell types within our nervous system
Neurons (first 3 =main)
*Bipolar cell (have two processes e.g retina)
*Pseudo-unipolar(short single process that branches like a T, neurons within the PNS
*Multipolar cell (several dendrites, 1 axon majority of cells in CNS
-Pyramidal cell of hippocampus
-Purkinje cell of cerebellum
Glia (Main ones (CNS))
*Astrocytes
*Microglia (these enter the CNS to become resident glia)
*Oligodendrocytes
Five shared features of neurons
- Same structural components of individual nerve cells
2.The mechanisms by which neurons produce signals within and between nerve cells
3.The patterns of connections between nerve cells and between nerve cells and their targets: muscle and gland effectors
4.The relationship of different patterns of interconnection to different types of behaviour
5.How neurons and their connections are modified by experience
What is the basic structure of neurons
Cell Body (Soma): The cell body is the central part of the neuron, containing the nucleus and most of the cellular organelles. It plays a crucial role in maintaining the neuron’s overall function.
Dendrites: Dendrites are branching extensions that emanate from the cell body. These structures receive incoming signals from other neurons or sensory receptors and transmit these signals toward the cell body.
Axon: The axon is a long, slender, and tubular projection that extends from the cell body. It is responsible for transmitting electrical impulses (action potentials) away from the cell body to other neurons, muscle cells, or glands.
Myelin Sheath: Some axons are covered by a fatty insulating substance called myelin, which acts as an electrical insulator. Myelin sheaths are produced by glial cells and help to speed up the transmission of electrical signals along the axon. In between the myelin sheaths, small gaps or nodes of Ranvier are present, where the axon is exposed.
Axon Terminals (Axon Endings): At the end of the axon, there are numerous small branches and specialized structures called axon terminals. These terminals form synapses, which are junctions where the neuron communicates with other neurons or target cells. Neurotransmitters are released from axon terminals into the synapse to transmit signals to the next cell.
Synapse: The synapse is a small gap between the axon terminal of one neuron and the dendrites, cell body, or axon of another neuron. It is where the transfer of information occurs through chemical signaling, as neurotransmitters are released from one neuron and bind to receptors on the target neuron.
Dendrites–>Cell Body (Soma)–>Axon–>Myelin Sheath–>
Nodes of Ranvier–>Axon Terminals–>Synapse–> Neurotransmitters.
Microtubules run north to south
Astrocytes
Highly specialised ‘star-like’ cells
Two main types:
Fibrous
White matter
Long non-branched processes with endfeet involved in Ranvier’s nodes
Protoplasmic
Gray matter
Highly branched processes that involve synapses, and whose endfeet cover the blood vessel (important in BBB)
They are very connected cells, they have Perisynaptic astrocytic processes (PAPs).
Mouse: a single astrocyte can cover up to 100,000 synapses
Human brain that number is more than one million!
What are Astrocytes functions?
ACTIVE Primary role is trophic, metabolic and protective support of CNS (neurons)
Ionic homeostasis
*Recycling neurotransmitters (modulation of synaptic activity)
Supply mitochondria to neurons
Regulation of cerebral blood flow
*Maintenance of BBB
Respond to injury
Promote repair
Inflammatory Mediator in astrocytes
When there is no injury and there is no need for inflammation they are in a homeostatic state so processes are simple however if they are activated, they increase branching and have an increased production of Glial fibrillary acidic protein (GFAP).
When they are activated they can either be
Pro-inflammatory (A1)
-Induce transcription of pro-inflammatory genes e.g TNFa
Anti-inflammatory signalling (A2)
-inhibits transcription of inflammatory factors
How do astrocytes respond to injury?
Astrocyte Activation: They can change their morphology and become hypertrophic, meaning they enlarge and extend their processes. This response helps create a barrier to contain the damage and prevent the spread of inflammation to healthy tissue.
Formation of the Glial Scar: Astrocytes play a crucial role in forming a glial scar, which is a dense network of astrocytic processes that acts as a physical barrier around the site of injury. While the glial scar helps isolate the damaged area, it can also hinder axonal regeneration, which can be a drawback in terms of functional recovery.
Release of Growth Factors and Cytokines= These molecules can have both neuroprotective and inflammatory effects.
Uptake of Neurotransmitters and Toxins=assist in clearing cellular debris and toxins generated by the injury.
Expression of Glial Fibrillary Acidic Protein (GFAP): used as a marker for astrocyte activation
Modulation of the Blood-Brain Barrier (BBB)=disruption and repair of the BBB, affecting the permeability of substances into the brain.
Describe Microglia
Highly specialized cells; Micro = small, glia = glue
0.5–16.6% of the total cell population in the human brain
(more in grey matter than white matter)
They are born from myeloid origin (yolk sac), but enter the CNS very early in development and reside in the CNS
In PNS, macrophages have the same role as microglia in the CNS
Peripheral macrophages can enter CNS and become tissue resident microglia in later life (almost indistinguishable from ‘native’ microglia)
What are the roles of microglia?
First Responders! Always sensing the environment
Immune sentinels that are capable of orchestrating a potent inflammatory response (control CNS)
Have major roles in:
Synaptic organization (pruning)
Trophic neuronal support during development
Phagocytosis of apoptotic cells in the developing brain
Myelin turnover
Control of neuronal excitability
Phagocytic debris removal
Brain protection and repair.
They are highly dynamic cells
Physiological State
Number and function tightly controlled by the local microenvironment and by interactions with surrounding cells.
Have a close interaction with neurons, astrocytes and oligodendrocytes.
Pathological Insult
Phenotype is disease-dependent
Shift into different functional states
Modify proliferation, morphology (i.e., shortened processes) and phagocytic activity
Become antigen presenting cells
Release of inflammatory factors such as cytokines and chemokines
M1: Classically activate (pro-inflammatory)
M2: Alternatively activated (anti-inflammatory)
They shift between the two states aren’t necessarily in one or the other
Describe Oligodendrocytes
*Myelinating cell of the CNS only
Purpose of myelin is permit fast saltatory nerve conduction
Myelin also protects and provides trophic support to an axon
*A single oligodendrocyte can form up to 50 myelin segments
Number of myelin segments determined by intrinsic and extrinsic controls
Play an important role in diseases such as Multiple Sclerosis
Have an active progenitor population present in the adult brain that is capable of repair (remyelination)
oligodendrocytes can myelinate multiple axonal segments from different neurons. This is one of the key differences between myelination in the CNS and PNS.
Describe Schwann cells
Schwann cells are the myelinating cells of the PNS
Function of myelin in PNS to also facilitate fast nerve conduction
Axons >1µM are sorted (radial sorting), ensheathed and myelinated by Schwann cells
1 Schwann cell makes one myelin segment
Number of myelin wraps determined by axon thickness and neuroregulin 1 (this is not the case for the CNS)
Capable of regeneration and remyelination
Oligodendrocyte vs Schwann Cell
Why are there two cell types that perform the same function?
Cells are derived from distinct cellular origins
Oligodendrocytes are born from Neural Stem Cells (Ectoderm)
Schwann cells are born from Neural Crest
Oligodendrocytes will only myelinate in the CNS*
*Not true for in vitro co-culture, will myelinate dorsal root ganglia (PNS)
Schwann cells will not cross into the CNS, however if transplanted, can remyelinate.
Is it a space thing? Oligodendrocytes capable of multiple wraps in the brain to save on space??
can you describe a simple knee reflex?
Hammer tap stretches tendon, which, in turn, stretches sensory receptors in leg extensor muscle
(A) Sensory neuron synapses with and excites motor neuron in the spinal cord
(B) Sensory neuron also excites spinal interneuron
(C) Interneuron synapse inhibits motor neuron to flexor muscles
(A) Motor neuron conducts action potential to synapses on extensor muscle fibers, causing contraction
(B) Flexor muscle relaxes because the activity of its motor neurons hasbeeninhibited
What about more complex movements?
Describe voluntary movements
We use the sensorimotor system
Sensory system: Touch
Receptive field of a touch-sensitive neuron: Gentle touches evoke action potentials
The area from which the sensation arises is called the perceptive field
A patch of skin contains many overlapping receptive fields – allowing sensations to shift smoothly from one neuron to the next
skin that has hair there is more spacing out of cells
Somatosensory System
*Dorsal column - medial lemniscal System
-Relay proprioception and discriminative (tactile) touch
Conveyed to the spinal cord and brain stem by large-diameter myelinated fibres
-Crosses through the spinal cord, through the brain stem and conveyed to thalamus and then the cerebral cortex
*Spinothalamic tract (Anterolateral System)
-Pain and temperature, non-discriminative touch /pressure.
Conveyed to the spinal cord by small diameter myelinated and unmyelinated fibres
-Crosses through the spinal cord, through the brain stem and conveyed to the thalamus and then to the cerebral cortex.
Pathways for the visual system
eye signal travels up optic nerve going up to thalamic nuclei which signals to primary visual cortex and then goes to
Parietal lobe: visually guided movement and finally processed through temporal lobe: object recognition
The eye has to change to respond to light signals. It goes through Pretectum and is processed by going back through Ciliary ganglion to then dilate or constrict pupil
Information from retina sent to superior colliculus (SC) via optic nerve these follow though primary visual cortex and processed in posterior parietal cortex and then goes to frontal Eye Fields and feedback goes to the pons to initiate eye movement.
Divergence and convergence
The stretching of just one muscle activates several hundred sensory neurons, each of which makes contact with 40-50 motor neurons and this leads to two terms that we use in regard to pattern connection:
Divergence
One neuron (sensory) activates many target cells (motor neurons)
Important because a target motor neuron that can receive information from many sensory neurons is able to integrate information from many different sources
Convergence
One motor neuron receives many input contacts (sensory neurons)
Important because it ensures that a motor neuron is only activated if a sufficient number of sensory neurons become activated together
Somatic nerve fibres running to and from the periphery are collected together into bundles called peripheral nerves
Each nerve contains thousands of axons; each of which arises from a nerve cell body
Nerves are surrounded by layers of connective tissue:
Each nerve fibre surrounded by endoneurium
Nerve fibres are group into bundles (fascicles)
Fascicles surrounded by perineurium
Peripheral nerve surrounded by epineurium
One peripheral nerve contains sensory, motor and autonomic nerve fibres of varying size and myelination.
How are action potentials mediated?
Describe action potentials
Action potentials are mediated via ion channels:
Sodium (Na+) channels
Potassium (K+) channels
All-or-nothing event
Rapid sequence of changes in the voltage across a membrane
The membrane voltage (potential) is determined by the ratio of ions, extracellular to intracellular, and the permeability of each ion
The rapid rise in potential, depolarization, is initiated by the opening of sodium ion channels within the plasma membrane
The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels.
3 key stages: depolarisation, repolarisation and hyperpolarisation
What does the rate of conduction depend on?
The larger the diameter of the axon means the conduction of action potential is faster
Greater total volume for electrical currents to flow through (less internal resistance)
The plasma membrane has a greater number of ion channels
However current is still lost – therefore need for myelin
grey matter=Smaller calibre axons, unmyelinated so slower
White matter=Larger calibre axons, myelinated so faster
Conduction of an action potential along a nerve fibre is enhanced by myelin
Myelinated axons:
The sheath is interrupted at regular intervals by the nodes of Ranvier
The nodes contain a high concentration of Na+ channels allowing for regeneration of the action potential
Action potential described as ‘jumping’ between the nodes
This is called saltatory conduction
Unmyelinated axons:
Depolarization of the cell membrane must spread to the immediately adjacent region of the membrane, raising the potential passively until reaching the threshold voltage.
The action potential propagates as a continuous wave of depolarization.
Compound Action Potentials
Individual axons produce action potentials
Grouped action potentials i.e the sum of action potentials from a whole nerved is called a compound action potential
If a peripheral nerve is stimulated, the total electrical activity that results (the CAP) can be recorded between two external electrodes
Recording CAPs
Amplitude and shape of a CAP determined by:
Stimulus voltage
Diameter of axons in nerve
A CAP recording represents the sum of all action potentials that have fired at a given stimulus voltage
Smaller voltage – a CAP may be smaller as only a few axons are firing (others don’t reach threshold)
Large diameter axons reach threshold at lower voltages compared to small diameter axons
To measure CAPs in vivo, an electrical stimulation is given to the median nerve (at elbow),
The time taken for the abductor pollicis brevis muscle to contract is recorded using surface electrodes.
The recording is called an evoke potential or evoked CAP
