Nerve and Muscle Flashcards
What does the central nervous system consist of?
The brain and spinal cord which are both composed of neurons and glia.
What does the peripheral nervous system consist of?
Peripheral nerves and ganglia which is composed of neurons and glia.
What are neurons?
Specialised cells for transmission of information.
What are the functions of dendrites?
Receive input and send it to the cell body.
What are the functions of the cell body?
Contains the nucleus/organelles and aggregates input from the dendrites.
What are the functions of axons?
Transmit electrical impulses. Can be myelinated.
What are the functions of axon terminals?
Releases neurotransmitters
What is the input zone?
Consists of the dendrites and the cell body
> Receives chemical signals from other neurons.
What is the summation zone?
Consists of the axon hillock (start of the axon)
> Summates input
What is the conduction zone?
Consists of the axon
> Transmits electrical signals:
1 - both ways between the brain and spinal cord.
2 - from the peripheral sensory receptors.
3 - to effector cells.
What is the output zone?
Consists of the axon terminals
> Synapses on the input zone of other neurons or effect cells.
> Releases neurotransmitters
What are the 4 morphological types of neurons?
- Multipolar - multiple processes from the cell body.
- Bipolar - 2 processes from the cell body.
- Unipolar - 1 process from the cell body that branches into dendrites and axon.
- Anaxonic - no axon, all processes look identical.
What does glia do?
Supports neurons.
What are the features of the ependymal cell?
Line fluid-filled spaces in CNS that have cilia to circulate CSF
What are the features of the microglia?
> CNS
Immune cell
Engulf micro-organisms and debris
What are the features of astrocytes?
> CNS
Supply nutrients to neurons
Ensheath capillaries
Respond to injury
What are the features of oligodendrocytes?
Supports CNS nerve fibres and ensheathes them with myelin
What are the features of Schwann cells?
Support PNS nerve fibres and ensheaths them with myelin
What is the myelin sheath?
A layer of lipids that wraps around the axon, increases conduction velocity via nodes of Ranvier - gaps between myelin. The PNS and consists of multiple Schwann cells in a line.
Explain Synapses
An electrical signal triggers the pre-synaptic neuron to release neurotransmitters in synaptic vesicles from the axon terminals. They travel across the synaptic cleft to neurotransmitter receptors in the postsynaptic neuron.
What is afferent?
Ascending
IN to the brain
What is efferent?
Descending
OUT of the brian
What is somatic information?
Information that we are conscious of and can control. e.g voluntary muscle control and sensory information that we are aware of.
What is the composition of the somatic efferent division?
Consists of 2 myelinated neurons.
> The upper motor neuron - cell body in the brain and axon in the spinal cord.
> The lower motor neuron - cell body in the spinal cord and axon in the spinal nerve.
Why is the lower motor neuron considered the pre-synaptic cell?
Synapses onto the effector skeletal muscle via a synaptic cleft (NMJ) and use acetylcholine (Ach) as a neurotransmitter.
What is autonomic information?
Information that we are unaware of and cannot control.
E.g. involuntary muscle control and sensory information that we are unaware of.
What is the composition of the autonomic efferent nervous system?
Consists of 2 divisions (sympathetic & parasympathetic) and involves effectors such as smooth or cardiac muscle, glands and adipose tissue.
It consists of 3 neurons
> 1st: cell body in the brain and axon in the brain/spinal cord.
> 2nd: myelinated with a cell body in the CNS and axon extends in PNS, it synapses onto neurons.
> 3rd: in autonomic ganglion. Is unmyelinated with the cell body in the PNS and the axon extends in PNS and synapses on an effector organ.
Neuron 2 location in sympathetic NS
Short axon
Cell body in a thoracolumbar level of the spinal cord.
Neuron 2 (pre-ganglionic) location in the parasympathetic NS
long axon
cell body in cranial and sacral levels
Neuron 3 (post-ganglionic) location in the sympathetic NS
Long axon
Cell body close to CNS in sympathetic ganglion
Neuron 3 (post-ganglionic) location in the parasympathetic NS
Short Axon
Cell body distant from the CNS in parasympathetic ganglion in/near effector
Neurotransmitter form 2 to 3 in the sympathetic NS
Acetylcholine (ACh)
Neurotransmitter form 2 to 3 in the parasympathetic NS
Acetylcholine (ACh)
Neurotransmitter 3 to effector in the sympathetic NS
Norepinephrine (NE)
Neurotransmitter 3 to effector in the parasympathetic NS
Acetylcholine (ACh)
Function in the sympathetic NS
Prepares the body for acute or stress response.
“fight or flight” system
Function in the parasympathetic NS
Prepares the body for the restful situations
“rest and digest” system
Effects of the sympathetic NS
> Increased heart rate > Decreased gastric motility > Decreased salvination > Increased pupil size > Increased sweating >Increased blood flowto muscles
Effects of the parasympathetic NS
> Decreased heart rate
Increased gastric motility
decreased pupil size
Increased salivation
What is the sympathetic chain ganglia?
Sit where pre-ganglionic neurons synapse onto the input zone of the post-ganglionic neurons. Found on each side of the vertebral column and has 21-23 pairs.
What is an action potential?
Information travelling along the membrane of a nerve cell associated with the generation of electrical impulse. They reach a threshold at the axon hillock, an AP will travel down the axon.
What is propagation?
Occurs when voltage-gated Na+ channels open at the axon initial segment.
The function of voltage-gated ion channels
Open when there is a charge in the membrane potential (activation gate) but can close when the membrane potential is too high (inactivation gate).
What are the voltage-gated channels doing at the resting membrane potential?
Closed
Explain action potentials
- Depolarisation to threshold (-60mV)
> Local change in MP is sufficient to depolarise the cell
> Voltage-gated Na+ channels begin to open - Activation of Na+ channels and rapid depolarisation (+10mV).
> Voltage-gated Na+ channels are open
> Na+ ions flowing into the cell
> membrane rapidly depolarises - Inactivation of Na+ ion channels and activation of K+ ion channels (+30mV)
> membrane fully depolarised
> sodium ion channels inactivate
> voltage-gated potassium channels open - K+ ion channels close
> Membrane repolarises to RMP
> Na+ and K+ channels are closed
Define Absolute refractory period
In a period where a second action potential can’t be activated, Sodium channels will not reactivate until hyperpolarisation occurs.
Relative refractory period
A period where a second action potential cannot be activated unless there is a significant stimulus. Sodium channels begin to reactivate to return to RMP.
What is AP propagation - unmyelinated axons?
- AP develops at the initial segment, MP depolarises to +30mV
- Na+ ions spread away from the open voltage-gated channels, graded depolarization brings segment 2 to aa threshold.
- AP develops in segment 2, the initial segment starts repolarising and is refractory.
- Na+ ions spread to segment 3 causing graded depolarization to bring segment 3 to threshold, the initial segment still refractory.
What is AP propagation - myelinated axons?
- AP develops at the initial segment, then jumps from node to node.
- Local current produces graded depolarization that brings the axolemma at node 1 to the threshold.
- An AP develops at node 1, the initial segment starts repolarising and is refractory.
- local current produces graded depolarization that brings the axolemma at node 2 to the threshold.
What is the composition of the spinal cord?
Long continuous structure made up of white and grey matter in the CNS and nerve roots and ganglion makes up the PNS.
Found within a meningeal sac that is filled with cerebrospinal fluid (CSF). The end of the spinal cord tappers into the conus medularis which is made up of non-neural tissue. The coins medulris is attached to the filum terminal to act as an anchor and is made up of fibrous tissue.
Where are meninges found?
encasing the brain and in the spinal cord.
What is Dura matter?
> The most superficial layer of the meninges.
It is dense and fibrous - tough
Consists of 2 layers - outer and inner
Inner layer can fold in on itself = dural folds
What are venous sinuses?
Tough mother
Spaces formed when the inner and outer dura mater separates. They are collecting veins that collect venous blood from the brain and old CSF.
What are dural folds?
Sperate major divisions of the brain and provide stability.
What are the 3 dural folds?
- falx cerebri - separates cerebral hemisphere in the median plane.
- Falx cerebelli - separating cerebellar hemisphere in the median plane.
- Tentorium cerebelli - separates the cerebrum and cerebellum in the horizontal plane.
What is Arachnoid matter?
spider-like mother
> Inferior to the dura mater
Superior to the pia mater
Contains blood vessels that lie on the pia mater
Does not extend into the sulci
CSF filled space between the arachnoid and pia mater.
What are arachnoid granulations?
perforations of the inner layer of dura mater that drain the old CSF from the subarachnoid space to the venous sinus.
What is Pia Mater?
Delicate-mother
> Most deep layer
Transparent and delicate
Clings directly onto the brain following the gyri n extending into sulci
What is the ventricular system?
Network of interconnected spaces within the brain. The spaces are filled with CSF to provide nutrients to and protects the brain. these spaces are lined with ependymal cells which have cilia to circulate CSF.
What are the names of the ventricles?
> lateral ventricles - 2 one on each side of the cerebral hemisphere.
Third ventricle - located in the diencephalon connected to the 4th ventricle.
cerebral aqueduct - Connects 3rd to 4th ventricle located in the midbrain.
fourth ventricle - inferior to the cerebral aqueduct and located in the cerebellar.
central canal (spinal cord)
Where is the CSF found?
subarachnoid space surrounding the CNS.
How is CSF produced?
By the choroid plexus within the ventricles.
What is the function of CSF?
provide support and cushioning as well as transport nutrients and waste
What is the CSF circulation path?
> Starts at the lateral ventrilces > 3rd ventricles > cerebral aquduct > 4th ventricle > Subarcahnoid space > exits through arachnoid granulations into venus sinus.
What are the steps of synaptic transmission? 5
- Action potential triggers the opening of voltage-gated Ca2+ channels
- Calcium ions diffuse into the axon terminal triggering synaptic vesicles to release acetylcholine by exocytosis
- Acetylcholine diffuses across the synaptic cleft, binds to ACh-gated sodium ion channels, producing graded depolarisation – EPSP (Excitatory postsynaptic potential)
- Depolarisation ends as acetylcholine is broken down into acetate and choline by AChE
- Axon terminal reabsorbs choline from the synaptic cleft and uses it to synthesise new acetylcholine molecules
Define EPSP
A minor depolarisation
How does EPSP occur?
Chemical stimulus opens sodium ion channels, the stimulus is removed and excess sodium ions are transported out of the cytosol
Define IPSP
A minor hyperpolarisation
How does IPSP occur?
Chemical stimulus opens potassium ion channels, the stimulus is removed and excess potassium ions are transported out of the cytosol.
What happens if an IPSP and EPSP occur at the same time?
they cancel out therefore there is no change in the membrane potential.
What happens if multiple EPSP’s happen at once?
Membrane potential becomes much more positive, causing an action potential
What is the synaptic transmission at the NMJ?
Excitatory and absolute - there is no axon hillock and no EPSP/IPSP summation.
What are the 2 types of summation?
Temporal
Spatial
What is temporal summation?
Time - one stimulus will not depolarise the membrane enough to reach the threshold, however, a second (or multiple) stimuli coming from the same place will be sufficient to depolarise the membrane to the threshold, allowing propagation of an action potential.
What is Spatial summation?
Space - two stimuli occur at the same time at different places of the neuron, individually, these stimuli would not be sufficient to reach the threshold, but when added together they reach the threshold allowing propagation of an action potential.
What is the foramen magnum?
Spinal cord starts here, opening at the base of the skull
What is the inferior border of L1?
Where the spinal cord ends
How many vertebrae are in each section?
Cervical - 8 Thoratic - 12 Lumbar - 5 Sacral - 5 Coccygeal - 1
Where is the spinal cord found?
Within the meningeal sac that is filled with cerebrospinal fluid (CSF).
Where does the meningeal sac fit?
Inside the spinal cavity within the spinal canal of the vertebrae.
Where does the spinal cord end?
Conus Meduaris - it tappers into a cone shape
What is the Conus meduaris made up of?
non-neural tissue
What does the conus meduaris extend to?
Filum terminale - bottom of the spinal cavity
What is the function and makeup of the filum terminle?
Anchor the spinal cord and made up of fibrous, non-neural tissue
How many pairs of spinal nerves are found in the spinal cord?
31 - determined by the vertebrae that they extend inferiorly to.
Where do spinal nerves exit?
At the vertebral column at the site that they originate
What is the Cauda equina?
Nerve bundles at the inferior end of the spinal cord.
Chemical gates ion channels open when a ___ binds, allowing ions to flow into the cell.
Neurotransmitter
At the NMJ, the neurotransmitter uses what?
acetylcholine
What happens when ACh binds to a chemical - gated channel?
Opens
What happens when ACh leaves a chemical - gated channel?
closes
What is a chemical synapse?
junction or gap between nerve cells (or a neuron and effector) where an action potential is transferred via a neurotransmitter. It is a control point for electrical information flow.
What is the white matter of the spinal cord split into?
Ventral, lateral and dorsal columns - which consist of axons
What makes up the spinal cord - CNS?
White and grey matter?
What makes up the spinal nerves - PNS?
Nerve roots and ganglion
What information does the dorsal half of the spinal cord control?
afferent and sensory - Information comes in from the PNS into CNS via the dorsal root ganglion and dorsal nerve roots.
What are sensory neurons?
unipolar - their cell bodies are found in the dorsal root ganglion
What is the input zone?
dendrites - associates with the receptors for the sensory stimulus of the body.
What is the output zone?
axon terminals - enter the spinal cord via dorsal roots
What information does the ventral half of the spinal cord control?
Efferent/motor - Information comes from the CNS into the PNS via ventral nerve roots and commands to effectors in the body
Where are the Somatic motor neuron cell bodies found?
ventral horn
Where are the autonomic neuron cell bodies found?
lateral horn
What information can the spinal cord carry?
afferent and efferent
What is the flow of information for the dorsal ramus?
efferent to posterior
afferent to posterior
What is the flow of information for the ventral ramus?
efferent to front
afferent from front
What is the function of the rami communicantes?
sympathetic, only at T1 and T2
What is the function of the frontal lobe?
> Language and personality (inferior and anterior)
> Motor control (superior/posterior)
What is the function of the parietal lobe?
somatosensory
What is the function of the occipital lobe?
Vision
What is the function of the temporal lobe?
Memory and hearing
What do the thalamus and hypothalamus make up?
Diencephalon
What makes up the brain stem? (3)
midbrain, pons and medulla oblongata
What are the 3 types of white matter in the brain?
- Commissural tracts
- Projection tracts
- Association tracts
What do the axons do in the commissural tract?
Cross side to side
What is an example of the commissural tract?
Corpus callosum
What do the axons do in the projection tract?
Travel between cortex and other non-cerebral CNS areas.
What is an example of the projection tract?
corticospinal tract
What do the axons do in the association tract?
Stay on the same side in the cerebral cortex
What is the purpose of the association tract?
Communication between brain areas (short and long distance)
What is the primary motor cortex?
Precentral gyrus
What determines the region of the body that is controlled?
The specific location of the upper motor neuron cell bodies
What happens if the motor cortex is damaged?
muscle weakness or paralysis in the part of the body which that region controlled.
What makes up the corticospinal pathway?
2 neurons between the brain and skeletal muscles.
Where is the cell body location for the upper motor neuron?
Primary motor cortex (precentral gyrus)
Where is the cell body location for the lower rotor neuron?
Ventral horn (grey matter) of the spinal cord.
Where is the axon location for the upper motor neuron?
Extends from the motor cortex to the other side of the spinal cord
(crosses over in the medulla oblongata)
Where is the axon location for the lower motor neuron?
Extends out of spinal cord (ventral root) into body
Where is the synapse location for the upper motor neuron?
Lower motor neuron
Where is the synapse location for the lower motor neuron?
Skeletal muscles
What is the primary somatosensory cortex?
postcentral gyrus
What determines the region of the body that sensory information is received from?
The specific location of the neuron cell bodies.
What happens if the somatosensory cortex is damaged?
They will not sense information from the region of the body it corresponds to.
How many neurons does the dorsal column pathway consist of?
3
Where is the cell body location of neuron 1?
Dorsal root ganglion
Where is the cell body location of neuron 2?
Medulla oblongata
Where is the cell body location of neuron 3?
Thalamus
Where is the axon location of neuron 1?
Peripheral fibre: towards the sensory receptor
Central fibre: towards brain via dorsal columns
Where is the axon location of neuron 2?
Crosses over in medulla oblongata and ascends
Where is the axon location of neuron 3?
Ascends to the somatosensory cortex
Where is the synapse location of neuron 1?
Neuron 2 in medulla oblongata
Where is the synapse location of neuron 2?
Neuron 3 in the thalamus
Where is the synapse location of neuron 3?
On cell body of somatosensory cortex neuron
What is a reflex movement?
reproducible, automatic response to a certain stimulus
What are examples of reflex movements?
stretch and withdrawal
What are spinal reflexes?
organised neural circuit contained within the spinal cord (does not extend into the brain).
What does the stretch reflex utilise?
a structure called the muscle spindle, which shortens (contracts) when the reflex occurs
What is the muscle spindle important for?
posture
What is the makeup of the muscle spindle?
contains intrafusal fibres that are innervated by gamma motor neurons and sensory neurons that have dendrites spiralling around the centre of the intrafusal fibres.
What is the process of the spinal reflex?
- Stimulation of a receptor - muscle spindle elongates/stretches
- Activation of a sensory neuron
- Information processing in the CNS (spinal cord)
- Activation of a motor neuron
- Response of a peripheral effector (skeletal muscle fibres)
What is the withdrawal reflex?
sensing of a painful stimulus that travels via a sensory neuron to the spinal cord. Reciprocal inhibition occurs, in which flexors are stimulated and extensors are inhibited
How can control of muscle tension be achieved?
> Motor unit recruitment - more motor units therefore more muscles fibres activated leading to more tension
Stimulation frequency - If Ap’s are more frequent, then max tension is reached faster and a smoother tension is developed.
What is involved in the preparing and performing of movement?
cerebellum
What coordinates muscles and maintains gaze?
cerebellum
Where does the decision to perform voluntary movement arise in?
The frontal lobes then travels to the premotor cortex then to the cerebellum
What does the cerebellum do when performing a movement?
compares the intended movement with the actual result via the use of senory feedback then sends the adjustments to the primary motor cortex.
What is ataxia?
Deficits of the cerebellum
What is the voluntary motor control loop?
> Planning of the voluntary muscle control occurs in the cerebellum
information sent to the motor cortex which activates the lower motor neurons in the spinal cord to produce movement.
Muscle spindles monitor muscle movement and body positioning and provide sensory feedback to the brain.
What is pseudounipolar?
one axon that splits into two branches, one extending peripherally and the other centrally
What are the special senses for CNS input?
> Vision > Hearing > Taste > Smell > Balance (vestibular)
What are the somatic and visceral sensations for CNS input?
> Touch
Pain
Temp
body position
What are sensory receptors?
Highly sensitive to particular stimuli. Will activate different sensory receptors.
What are sensory receptors?
sensory endings of afferent neurons or specialised receptor cells
What are the 4 types of information that describe a sensory stimulus?
- Modality
- Intensity
- Duration
- Location
What is modality?
The type of sensory receptor activated.
What is intensity?
Frequency of AP firing in an afferent neuron
What is the duration?
duration of an AP firing in an afferent neuron
What is the location?
location of the sensory receptor(s) activated, ‘mapped’ in brain
What are the factors for modality?
- Proprioception – via the muscle spindle, detects muscle length, body position, movement and posture.
- Touch – a variety of forms, functions and receptive fields.
What are the factors for the intensity?
- If stimulus intensity increases so do the frequency of APs
- If not very intense, afferent neurons may provide no response due to the threshold not being reached
- Intense stimuli can also activate a higher number of receptors, thus more APs in sensory axons
What are the factors for the duration?
• Sensory receptors often adapt to the stimulus, a continued stimulus will cause decreased output (reception) over time.
What are the factors of the location?
- The region of space in which a receptor can detect a stimulus is known as the receptive field
- When these fields are small and dense, stimuli are easily discriminated
- When fields overlap, multiple receptors may detect a single stimulus
What is transduction?
When sensation is consciously detected by a sensory receptor a sensory stimulus is converted to action potentials
What happens after transduction?
Receptors synapse with afferent neurons, which carry the action potential down their peripheral nerve via a sensory tract/pathway. This action potential is then integrated in the cerebral cortex, where sensation is perceived.
Where is sensation location and type is consciously identified in?
primary somatosensory cortex (postcentral gyrus)
Where is information perceived and interpreted?
somatic sensory association cortex (parietal lobe).
Areas of the somatosensory cortex are associated with…
specific areas of the body
Large regions of the cortex are associated with…
densely innervated areas of the body with small receptive fields
