Nerve and Muscle Flashcards
What are the two sections of the nervous system?
Central nervous system (CNS)
Peripheral nervous system including the ENS (PNS)
What makes up the CNS?
the brain and the spinal cord
What makes up the PNS?
nervous tissue outside the CNS such as cranial nerves and spinal nerves
What are the two general cell classes in the nervous system?
Neurons and glia
Describe the function of a neuron (nerve cell)
a cell specialised for the transmission of information
How many morphological types of neurons are there?
4
What are the morphological types of neurons
- multipolar
- unipolar
- bipolar
- anaxonic
Describe a multipolar neuron
- multiple dendrites
- single axon
- most common neurons in the CNS
Describe a bipolar neuron
Two distinct processes (one dendritic and one axonal) branching off the cell bod
Describe a unipolar neuron
- the dendrites and axon are continuous
- the cell body lies off to one side
Describe an anaxonic neuron
- no distinct axon
- difficult to determine what is the axons and which are the dendrites
Describe the function of glia
support for neurons
How many basic types of glia are there?
5
What are the basic types of glia?
In the CNS: - astrocytes - microglia - ependymal cells - oligodendrocytes In the PNS: - Schwann cells
How many basic types of glia are in the PNS and how many are in the CNS?
1 in the PNS
4 in the CNS
Describe an astrocyte and explain its function
- a type of glia in the CNS Function: - supply nutrients to neurons - ensheath blood capillaries - transmit information (this role has just been discovered)
Describe a microglia and explain its function
- a type of glia in the CNS
Function: - immune cells of the CNS
- engulf microorganisms and debris
Describe an ependymal cell and explain its function
- a type of glia in the CNS
Function: - lines the ventricles in the brain and spinal cord
- have cilia to circulate the cerebrospinal fluid (CSF)
Describe an oligodendrocyte and explain its function
- a type of glia in the CNS
Function: - support nerve fibres
- ensheath nerve fibres with myelin
Describe a Schwann cell and explain its function
- a type of glia in the PNS
Function: - support peripheral nerve fibres
- ensheath them with myelin
Describe myelin, including its function and where it comes from
A sheath made of lipid (fat) that is wrapped around the axon of a neuron.
It increases the conduction velocity of electrical impulses down the axon
In the CNS it comes from oligodendrocytes and in the PNS it comes from the Schwann cells (it is the plasma membrane of the Schwann cell)
In the CNS, a group of cell bodies is called
a nucleus (confusing)
In the CNS, a bundle of axons is called a
tract
In the CNS, a group of cell bodies in the cerebral cortex or spinal cord is called
Grey matter
In the CNS, a bundle of myelinated axons in the cerebral cortex of the spinal cord or cerebral cortex is called
white matter
In the PNS, a group of cell bodies is called a
ganglion (pl. ganglia)
In the PNS, a bundle of axons is called a
nerve
What is a nucleus?
A group of cell bodies in the CNS
What is a tract?
A bundle of axons in the CNS
What is grey matter?
A group of cell bodies in the cerebral cortex or spinal cord in the CNS
(cell bodies, unmyelinated axons, axon terminals, dendrites etc.)
What is white matter?
A bundle of myelinated axons in the cerebral cortex or spinal cord in the CNS
What is a ganglion?
A group of cell bodies in the PNS
What is a nerve?
A bundle of axons in the PNS
What is the function of the dendrites?
- receive input
- send info to the cell body
What is the function of the cell body?
- contains the nucleus and organelles
- sums input that it collects from the dendrites
What is the function of the axon?
- carries electrical impulses
What is the function of the axon terminal?
- at the end of the axon
- neurotransmitter release
What are the Nodes of Ranvier?
- the gaps in between myelin in a neuron in the PNS (in between Schwann cells)
What is the input zone?
- dendrites and cell body
Describe the function of the input zone
- receives chemical signals from other neurons
What is the summation zone?
- the axon hillock
Describe the function of the summation zone
- decides whether or not it will pass on information
ie. whether to transmit the signal any further
What is the conduction zone?
- the axon (this could be quite long)
Describe the function of the conduction zone
messages in the form of action potentials are conducted to other cells via the axon
What is the output zone?
the axon terminals
Describe the function of the output zone
release of neurotransmitter to pass message on to other cells via the axon terminals
Presynaptic neuron
neuron before the synapse
What is the function of the presynaptic neuron?
releases neurotransmitter from axon terminal
Postsynaptic neuron
neuron after the synapse
What is the function of the postsynaptic neuron?
contains receptors for the neurotransmitter
What is a synaptic cleft?
the space where the synapse happens
What is somatic efferent information?
Give an example
Voluntary muscle control (eg. contraction of a skeletal muscle)
What is somatic afferent information?
Give an example
Sensory information we are aware of (eg. what we can see, hear, smell, feel)
What is autonomic efferent information?
Give an example
Involuntary muscle control (eg. contraction of the cardiac muscles producing and controlling heartbeat)
What is autonomic afferent information?
Give an example
Sensory information we aren’t aware of (eg. blood pressure)
Describe the upper motor neuron
- one of the myelinated neurons between the brain and the effector (skeletal muscle) in the somatic efferent division
- cell body in brain
- axon in spinal cord
Describe the lower motor neuron
- one of the myelinated neurons between the brain and the effector (skeletal muscle) in the somatic efferent division
- cell body in spinal cord
- axon in spinal nerve (carrying info between the spinal cord and the PNS)
What neurotransmitter is released in the somatic efferent nervous system at the synapse between the lower motor neuron and effector (skeletal muscle)?
Acetylcholine (ACh)
How many neurons are between the brain and the effector in the autonomic efferent nervous system?
3
What are the possible effectors of the autonomic efferent nervous system?
smooth muscle
cardiac muscle
glands
adipose (fat) tissue
Describe neuron #1 in the autonomic efferent nervous system
- cell body in the brain
- axon in the brain or spinal cord (CNS)
Describe neuron #2 in the autonomic efferent nervous system
- cell body in the brain or spinal cord
- axon in the PNS
- myelinated axon
Describe neuron #3 in the autonomic efferent nervous system
- cell body in the PNS
- axon in PNS (autonomic ganglion - group of cell bodies in the PNS)
- un-myelinated axon extends to the effector
Is neuron #2 in the autonomic efferent nervous system myelinated or un-myelinated?
Myelinated
Is neuron #3 in the autonomic efferent nervous system myelinated or un-myelinated?
un-myelinated
Where is the synapse between neuron #2 and #3 in the autonomic efferent nervous system and what is the neurotransmitter?
Synapse at autonomic ganglion
Neurotransmitter = ACh
Where is the synapse between and the effector organ in the autonomic efferent nervous system and what is the neurotransmitter?
Synapse at effector organ
Neurotransmitter = ACh or norepinephrine (NE)
In the synapse between neuron #2 and #3 in the autonomic efferent nervous system, which neuron is the pre-ganglionic neuron?
Neuron #2
and neuron #3 is the post-ganglionic neuron
What are the two subdivisions of the autonomic efferent nervous system?
Sympathetic
Parasympathetic
Describe the sympathetic division of the autonomic nervous system
- prepares the body for stress responses
- “fight or flight” system
Effects include: - increased heart rate
- constricting blood vessels to skin and viscera (internal organs)
- increasing blood flow to muscles
- decreased gastric motility
- decreased salivation
- increased pupil size
- increased sweating
Describe the parasympathetic division of the autonomic nervous system
- prepares the body for restful situations
- “rest and digest” system
Effects include: - decreased heart rate
- increased gastric motility
- decreased pupil size
- increased salivation
Describe the sympathetic nervous system synapse between neurons #2 and #3 (including neurotransmitter release)
- cell body in CNS
- pre-ganglionic axon is SHORT and myelinated and in the PNS
- neurotransmitter released in autonomic ganglion is ACh
- the autonomic ganglion is CLOSE to the CNS
Describe the sympathetic nervous system synapse between neuron #3 and the effector (including neurotransmitter release)
- cell body in PNS (autonomic ganglion)
- post-ganglionic axon is LONG and un-myelinated and in the PNS
- neurotransmitter released in effector synapse is NE
Within the autonomic efferent pathway, what is the neurotransmitter that is released by the second neuron to the third neuron in the parasympathetic nervous system
ACh
Describe the parasympathetic nervous system synapse between neuron #3 and the effector (including neurotransmitter release)
- cell body in PNS (parasympathetic ganglion)
- post-ganglionic axon is SHORT and un-myelinated and in the PNS
- neurotransmitter released in effector synapse is ACh
In the sympathetic nervous system, the axons of pre-ganglionic neurons (neuron #2) leave the CNS at
Thoracolumbar level of the spinal cord
In the sympathetic nervous system, the synapse and cell body of the post-ganglionic neurons (neuron #3) are in
the sympathetic ganglion
Describe the sympathetic chain ganglia
- collection of cell bodies linked together as a chain
- 21-23 pairs of cell bodies
- alongside the vertebral column
- place where the pre-ganglionic axon (neuron #2) synapse with the post-ganglionic axon (neuron #3)
- an axon comes away from the spinal cord (CNS) and it synapses here onto another neuron which then travels to the periphery
In the parasympathetic nervous system, the axons of pre-ganglionic neurons (neuron #2) leaves the CNS at the
cranial (brain stem) and sacral (spinal cord) levels
Where does the spinal cord start and end?
Starts at the foramen magnum
ends at the inferior border of the 1st lumbar vertebra (L1)
Where does the spinal cord sit?
Within the meningeal sack that fits inside the spinal cavity which is within the vertebra
At the end of the spinal cord, there is the
tapered cone of non-neural tissue called conus medularis
What is the conus medularis?
tapered cone of non-neural tissue at the end of the spinal cord
Between the conus medularis and the end of the spinal cavity is the
Filum terminale
What is the filum terminale?
Fibrous, non-neural tissue that extends from the conus medularis to the end of the spinal cavity to anchor the spinal cord
Where do the spinal nerves exit the vertebral column?
At the level that is appropriate to their origin eg. nerves originating in the lumbar spinal cord leave through the lumbar vertebrae.
Because the spinal cord finishes at the L1 vertebra, some of the spinal nerves have to extend lower than the spinal cord which creates a tail of spinal nerves.
How many segments does the spinal cord have?
31
How many pairs of spinal nerves come off each segment in the spinal cord?
one pair (left and right)
What is the Cauda Equina?
The large collection of nerves inferior to the spinal cord
Axons (myelinated or un-myelinated) are covered with
endoneurium
Endoneurium covered axons are bundled together to form a
Fascicle
Fascicles are covered with
Perineurium
Fascicles are bundled together to form a
nerve
Nerves are covered with
epineurium
What are the 3 protective coverings of the brain?
Dura mater
Arachnoid
Pia mater
The collective name for the 3 protective coverings of the brain is
the meninges
What are 5 features of the dura mater?
- outer-most layer of meninges
- dense and fibrous (tough) so that if there is a head injury, skull fragments do not penetrate the brain
- two layers
- the space between the two layers forms venous sinuses in some places
- the inner layer forms dural folds
Describe the dural folds and include their function
- formed from the inner layer of the dura mater
- separates major divisions of the brain
- provides stability of the brain within the cranium
What are the 3 dural folds and where are they located?
- Falx cerebri (separates cerebral hemispheres)
- Falx cerebelli (separates cerebellar hemispheres)
- Tentorium cerebelli (separates the cerebrum from the cerebellum)
What are 3 features of the venous sinuses?
- located where the two layers of the dura mater separate
- collecting veins
- They collect two things:
1. venous (deoxygenated) blood from the brain
2. ‘Old’ CSF after is had cycled through the ventricular system
What are 5 features of the arachnoid mater?
- layer beneath the dura mater
- layer above the pia mater
- does not extend into sulci (‘valleys’)
- contains two anatomical features:
1. subarachnoid space
2. arachnoid granulations - contains blood vessels (within the subarachnoid space, lying on top of the pia mater)
What are the four lobes in the brain called?
- frontal lobe
- parietal lobe
- occipital lobe
- temporal lobe
What are three ways to identify which is the anterior and which is the posterior aspects of the brain?
- the posterior aspect is more pointy
- the cerebellum is at the posterior aspect
- the anterior aspect has a C shape from the lateral view
What is a sulcus?
a furrow/valley in the brain
What is a gyrus?
a hill in the brain
What is a big/fat/deep sulcus called?
a fissure
What are the four sulci called?
- Central sulcus
- Lateral sulcus
- Parieto-occipital sulcus
- Transverse fissure
Where is the Central sulcus?
separating the frontal and parietal lobes
Where is the lateral sulcus?
separating the temporal lobe from frontal and parietal lobes
Where is the Parieto-occipital sulcus?
separating the occipital and parietal lobes
Where is the Transverse sulcus?
separating the cerebrum and cerebellum
What are the function(s) associated with the frontal lobe (and location)?
Lower frontal lobe: - language - personality - emotion - consequences of action Upper frontal lobe, closer to the parietal lobe: - efferent motor control
What are the function(s) associated with the parietal lobe?
somatosensory
Define somatosensory
Position of your body and touch on your skin
What are the function(s) associated with the occipital lobe?
vision
What are the function(s) associated with the temporal lobe?
hearing
memory
What three sections make up the brainstem?
- midbrain
- pons
- medulla oblongata
Seen from a medial view, what is the corpus callosum?
Bundles of axons (in the cerebral cortex or spinal cord in the CNS) underneath the cerebral cortex
Seen from a medial view, where is the diencephalon?
Underneath the corpus callosum
the third ventricle would sit between the diencephalon on each part of the brain
What are the two parts of the diencephalon called and which is the most superior?
Thalamus (superior)
Hypothalamus (inferior)
Seen from a coronal view (slices of bread), the cerebral cortex is _______ and it is located
grey matter (a group of cell bodies in the cerebral cortex or spinal cord) located at the edges of the brain
Seen from a coronal view (slices of bread), where are the deep nuclei in the brain?
underneath the lateral ventricles
What are the three types of white matter in the brain called?
- Commisural tracts
- Projection tracts
- Association tracts
Describe the commisural tracts, explain their function and give an example:
- Neurons with cell bodies in the cerebral cortex (grey matter) have their axons crossing over to the other side of the brain
- eg. corpus callosum
- this is how the right and left side of the brain and therefore right and left sides of the body can be coordinated
Describe the projection tracts and give an example:
- neurons with cell bodies in the cerebral cortex but their axons extend between the cortex and other CNS areas outside the cerebrum
- eg. corticospinal tract
Describe the association tracts, explain their function and give an example:
Tracts of axons that stay on the same side of the brain connecting to different areas of the cerebral cortex (eg. info going between occipital and frontal lobe)
eg. short or long distance
Where is the primary motor cortex?
The pre-central gyrus (the gyrus before the central sulcus)
Where is the primary somatosensory cortex?
The post-central gyrus (the gyrus after the central sulcus)
Describe the corticospinal tract:
Two neurons between the brain and effector:
- Upper motor neuron
- Lower motor neuron
Upper Motor Neuron (neuron #1):
- cell body in primary motor cortex (pre-central gyrus)
- axon extends from motor cortex to the spinal cord on the OPPOSITE site
- makes synapse on lower motor neuron
Lower Motor Neuron (neuron #2):
- cell body in ventral horn (grey matter) of spinal cord
- axon extends out of the spinal cord (ventral root) into body
- makes synapse onto skeletal muscle
The primary motor cortex controls
specific regions of the body
The primary somatosensory cortex controls
the receiving of sensory information from different regions of the body
Give some examples of the things that the primary motor cortex controls
moving toes
moving fingers
moving lips
Describe the consequence of damage to the motor complex:
Upper motor neuron in the primary motor complex is controlling the lower motor neuron to control the muscles to move the fingers.
If there was damage to the motor complex, the UMP would not function so that person can not more their fingers
The neurons in the post-central gyrus functioning as the primary somatosensory cortex are ______ information
receiving
What does the corticospinal tract describe?
The movement of information from the primary motor cortex (pre-central gyrus) to the skeletal muscle
What does the dorsal/posterior column pathway describe?
The movement of information from the sensory receptor in the body to the primary somatosensory cortex (post-central gyrus)
Describe the consequence of damage to the somatosensory complex:
If a neuron in the somatosensory complex that receives information from dorsal column pathways dies then:
- the ascending information has no place to go
- there is no perception of touch in that part of the body
Describe the dorsal/posterior column pathway:
Three neurons between the sensory receptor and the primary somatosensory cortex (post-central gyrus) :
Neuron 1:
- cell body in the dorsal root ganglion (unipolar neuron)
- peripheral fibre (input zone) from sensory receptor in skin
- central fibre (output zone) ascends towards brain in dorsal columns (spinal cord white matter)
- makes synapse on neuron #2 in medulla oblongata
Neuron 2:
- cell body in medulla oblongata
- axon crosses to the OPPOSITE SIDE and ascends
- makes synapse on neuron #3 in thalamus
Neuron 3:
- cell body in thalamus
- axon ascends to somatosensory complex
- makes a synapse on the cell body of a somatosensory cortex neuron
Then there is perception of touch
What are some internal features of the spinal cord?
- grey matter (cell bodies)
- white matter (axons)
- the central canal
- posterior (dorsal) sulcus
- anterior (ventral) median fissure
What are some internal features of the dorsal half of the spinal cord?
- Dorsal grey horn (cell bodies)
- Dorsal white columns (axons)
What are some internal features of the ventral half of the spinal cord?
- ventral grey horn
- ventral white columns
Where are the lateral grey horns (cell bodies)?
on the side of the grey matter in the spinal cord
Where are the lateral white columns (cell bodies)?
on the side of the white matter in the spinal cord
How can you distinguish between the dorsal nerve root and ventral nerve root?
the dorsal nerve root has the bump in it and the ventral nerve root does not
What are the dorsal and ventral nerve roots made of?
axons
What is the bump in the dorsal nerve root?
the dorsal root ganglion
What is the dorsal root ganglion made of?
cell bodies
Efferent/motor information travels from the ______ to the ______ through the ________ and the _________
CNS to the PNS
through the ventral grey horns and the ventral nerve roots
Afferent/sensory information travels from the ______ to the ______ through the ________ and the _________
PNS to CNS
through the dorsal grey horns and the dorsal nerve roots
The autonomic neurons (cell bodies) are located
in the lateral grey horns
the somatic motor neurons (cell bodies) are located
in the ventral grey horns
The ventral grey horn is _______ and the ____ leave and go to the rest of the body
cell bodies
axons
What is a consequence of damage to the somatic efferent neurons in the ventral grey horn?
Paralysis of muscles supplied by spinal nerves because no neuron is going out to command a skeletal muscle
How does information flow into the spinal cord?
information flows from the periphery into the dendrite (input zone) and then into the cell body (dorsal root ganglion) where an action potential is generated and information is sent through the axon to the dorsal part of the spinal cord (both grey horn and white matter) and then up to the brain
The dorsal root ganglia is cell bodies of neurons of what morphological type?
unipolar
What is a consequence of damage dorsal grey horn?
There would be a loss of sensation from regions of the body supplied by spinal nerves from this level on the same side only as information that would normally flow in the axons of the neurons are damage so is no more flow of info into the spinal cord
Does the spinal nerve carry efferent or afferent information?
both
What does the spinal nerve split into?
dorsal ramus and ventral ramus
What is the role of the dorsal ramus?
to carry both efferent and afferent information to and from the back
What is the role of the ventral ramus?
to carry both efferent and afferent information to and from the front of the body
What are two special features of the arachnoid mater?
- subarachnoid space
- arachnoid granulations
Describe the subarachnoid space
- between the arachnoid and pia mater
- filled with cerebrospinal fluid (CSF)
- where the blood vessels are located
Why is the subarachnoid space filled with CSF?
To protect the brain from banging against the skull
It helps cushion the brain
Describe the arachnoid granulations and include its function
- a feature of the arachnoid mater
- pierces the inner layer of the dura mater
- transports ‘old’ CSF into the venous sinus from the arachnoid space so it can go into the venous blood and be drained from the head
What is venous blood?
Deoxygenated blood
What are the four features of the pia mater?
- it is the inner layer of the meninges
- it is transparent and delicate
- blood vessels in the arachnoid sit on top of the pia mater
- sticks/adheres to the brain and follows the gyri and sulci
Do the meninges also surround the spinal cord?
yes
What are the four features of the ventricular system?
- a network of interconnected ‘spaces’ (ventricles) within the brain
- filled with CSF which nourishes the brain
- spaces are lined with ependymal cells which circulate CSF (waving cilia)
- the CSF is produced by the choroid plexus
What is the CSF produced by?
choroid plexus
the ventricles are lined with what type of cell?
ependymal
What is the purpose of the CSF?
to provide support and cushioning for the brain and to transport nutrients and waste
What is the purpose of the ependymal cells in the ventricles?
to line the ventricle and circulate the CSF by waving cilia
How many ventricles are there?
5
What are the names of the ventricles?
lateral ventricles (x2)
third ventricle
cerebral aqueduct
fourth ventricle
Describe the lateral ventricles
two C shaped spaces with a tail located in each hemisphere
Where is the third ventricle located?
in the diencephalon
Describe the cerebral aqueduct
- connects the third and fourth ventricles
- located in the midbrain
Where is the fourth ventricle?
at the level of the cerebellum
Describe the cerebrospinal fluid
- surrounds the central nervous system
- provides support and cushion
- transports nutrients and waste
- produced by the choroid plexus in the ventricles
Describe the circulation path of the CSF
Start:
- third ventricle
- into the cerebral aqueduct
- into the fourth ventricle
- then it enters the subarachnoid space
within the subarachnoid space it flows around the brain and spinal cord
- into arachnoid granulations into the venous sinuses and into the venous circulation
A reflex arc is an example of
a negative feedback loop
What are muscle spindles?
Types of stretch sensors that are receptors which are activated (depolarised) by an increase in muscle length (ie a stretch)
What do muscle spindles do?
Send information about stretch by initiating action potentials.
What are interneurons and where are they located?
They project up the spinal cord to higher centres, for conscious sensation and voluntary movement planning.
What is the purpose of the anterior/ventral root?
It is where the motor (efferent) information leaves the spinal cord
What does the ventral horn contain?
The cell bodies of motor neurons (their axons will travel out down the ventral/anterior root, along the spinal nerve and out to the body)
What is the purpose of the dorsal/posterior root?
Sensory information comes from the periphery and up the posterior root and it synapses in the dorsal horn. The axons of these nerves are unipolar and the cell body lies in the dorsal root ganglion
Describe the synapse at the sympathetic chain ganglia
An axon comes away from the spinal cord and it synapses onto another neuron which then travels to the periphery
Describe the corpus callosum including its function
The corpus callosum is a collection of axons in the CNS (ie. a tract). It is an example of a commisural tract.
Its purpose is to connect and communicate information between hemispheres
What two structures are in the diencephalon?
- thalamus
- hypothalamus
Describe the thalamus including its function
is an example of nuclei (a group of cell bodies in the CNS) and it acts as a relay station for information (sensory information that comes from the body to different parts of the brain)
What are 3 internal structures of the brain?
Cerebral cortex (grey matter) White matter (3 types) Deep nuclei
Describe somatic efferent division
- voluntary or involuntary movement?
- to or from the brain?
- how many neurons between the brain and effector and what are these called?
- are the axons myelinated or un-myelinated?
- what is the neurotransmitter that is released?
- what is the effector?
- voluntary movement
- efferent information (info away from the CNS)
- two neurons between the brain and the effector (UMN and LMN)
- axons are myelinated
- neurotransmitter is ACh
- effector is skeletal muscle
Muscles have stretch receptors called
muscle spindles
Muscles spindles are receptors that are activated (depolarised) by
an increase in muscle length
ie. a stretch
How do muscle spindles play a role in a muscle stretch reflex?
Muscle spindles send information about a stretch by initiating action potentials. These action potentials are conducted via sensory neurons in peripheral nerves through the dorsal root to the spinal cord. The sensory neuron axons are myelinated
What are two examples of spinal reflexes?
stretch reflex
withdrawal reflex
What do interneurons do (ie. where do they go)?
they project up the spinal cord to higher centres, for conscious sensation and voluntary movement planning
What is a reflex?
Automatic involuntary reaction to a stimulus resulting from a nerve impulse passing over a reflex arc
What is a reflex arc?
A neural pathway which can act on an impulse before that impulse reaches the brain
Describe a stretch reflex
When a physician taps (eg. the Achilles tendon) a tendon hammer, stretch receptors in the soleus muscle are stretched.
This stretch stimulates sensory neurons that extend to the spinal cord (the sensory neuron cell body is in dorsal root ganglion).
There is a synapse on to motor neurons that control the motor units in the stretched muscle. This occurs in the ventral horn.
An action potential is conducted down the motor neuron to the soleus muscle and there is a synapse between the motor neuron and the skeletal muscle at the NMJ. This results in concentric contraction of the soleus muscle so the foot briefly plantar-flexes
Each muscle spindle consists of a bunch of small, specialised muscle fibres called
intrafusal muscle fibres
Muscle spindles are involved in
a stretch reflex
maintaining normal upright posture
Describe a withdrawal reflex
When the pain receptors in your hand are stimulated, an action potential is propagated up the sensory neurons (cell body in the dorsal root ganglion).
The action potential activates interneurons in the spinal cord that stimulate motor neurons in the anterior grey horns. The interneurons also reports to the brain.
An action potential is conducted down the motor neuron which results in a contraction of flexor muscles (eg. the biceps brachii) that yanks your hand away form the hot stove.
However, there is also reciprocal inhibition
What is reciprocal inhibition?
When a specific muscle contracts, opposing muscles relax to permit the movement. When the flexors contract, the extensors relax and vice versa.
This means during a withdrawal reflex, (eg.) the action potentials propagated to the flexor muscles is excitatory which causes the bicep brachii to contract concentrically. However, there is also an inhibitory action potential is propagated to the extensors (the triceps brachii) which inhibits them
What are the basal ganglia?
a group of structures linked to the thalamus in the base of the brain and involved in coordination of movement
How does the brain prepare voluntary movement?
When you make a conscious decision to perform a specific movement, information is relayed from the frontal lobes to the premotor cortex. These areas in turn relay the information to the cerebellum and basal nuclei.
What are the roles of the cerebellum?
- What does it coordinate? How does it do this?
- It compares what with what?
- what does it help maintain?
- what does it help learn?
- coordinates muscles guided by sensory feedback
- compares intended movement with actual result
- helps maintain posture and gaze
- helps learn and automate movement
How does the cerebellum help coordinate movement?
By using information about current body position to compute movements needed to achieve a new body position (feedforward control) and to check planned movement against actual movements to compute corrections (feedback control).
How does the brain perform voluntary movement?
As the movement begins, the premotor cortex sends instructions to the primary motor cortex. Feedback from the basal nuclei and cerebellum modifies these commands, and output along the medial and lateral pathways directs involuntary adjustments in position and muscle tone.
Voluntary movement involves the activation or neurons in the
motor cortex
The motor cortex is anterior to the _________ of the cerebral hemispheres
central sulcus
Activation of the primary motor cortex is assisted by input from the
cerebellum and basal ganglia
The axons of the primary motor cortex neurons project to the
spinal cord
Primary motor cortex activation may occur as a result of
Internally generated movement plans
Externally cued movements
What are internally generated movements (ie. give an example)
You may decide to wiggle your foot for no reason
Where do internally generated movements arise from?
Activity in many brain regions including the prefrontal and medial prefrontal cortex
What are externally cued movements?
They are movements made in response to specific external cues eg. you may be instructed to wiggle your foot when you feel a touch
What triggers externally cued movements?
They are triggered by sensory information arriving from sensory pathways, via processing at the lateral premotor cerebral cortical area
Describe voluntary movement in response to an external stimulus:
- an action potential is initiated in the sensory “touch” neuron wherever the person is touched
- this is conducted up along the sensory axon into the spinal cord and up to the medulla
- here it synapses onto a secondary sensory neuron, initiating another action potential to conduct along that axon
- there is a synapse with a tertiary neuron in the brain
- eventually an action potential is initiated in a primary motor neuron
- this is conducted down the axon to synapse with the alpha motor neuron in the spinal cord
- the action potential initiated in the alpha motor neuron will conduct down the axon to a NMJ to cause a contraction of the skeletal muscle
What are the special senses? (5)
- smell (and pheromones)
- taste
- sight
- hearing
- vestibular (balance)
What are the somatic and visceral sensations? (4)
- touch
- pain
- warmth and cold
- body position (proprioception)
What are the two types of input to the CNS?
- special senses
- somatic and visceral sensations
What is the role of the sensory nerve endings?
to detect the mechanical length changes of the muscle overall
What are two ways that muscle tension is controlled?
- motor unit recruitment
- stimulation frequency
What is a motor unit?
A motor unit and the muscle fibre associated with them
How does motor unit recruitment affect the way muscle tension is controlled?
Fine control reflected in the number of axons innovating that muscle and in the size of the motor units (small motor units and small fibres = finer control)
If we want more power and more forceful contraction, we bring on board more motor units
How does stimulation frequency affect the way muscle tension is controlled?
The frequency at which action potentials are arriving at neuromuscular junction to activate muscle tension development can also control how much tension is being generated by the muscle overall. Modulating the amount of tension each of them individually generated by controlling the stimulation frequency
Where do we plan to make movement (goal-setting behaviour)?
The prefrontal lobe
Describe how we plan to make a movement to making a movement
The prefrontal lobe is responsible for planning movement. It feeds into the premotor cortex so we can start muscle contractions and movements
This information goes to the cerebellum which has access to all the sensory input that we need to know about where our bodies are in terms of position and space. The cerebellum therefore starts to help us organise the contractions of the muscles in a very specific way given the environmental conditions that exist. With the basal ganglia encouraging goal achieving movement, the cerebellum alerts the primary motor cortex sends output to lower motor neurons to recruit motor unit as required (the cerebellum continues to monitor balance and equilibrium and adjusts upper motor neuron activity)
What is the role of the basal ganglia?
it keep track of what muscle contractions have been useful in the past for similar goals and sends reward signals to activate those pathways when we are ready to achieve them
What are the sensory receptors for the somatic and visceral sensations?
the sensory ending of an afferent neuron
What are the sensory receptors for the special senses?
specialised receptor cell
What is transduction?
When the sensory receptor converts whatever type of energy it receives (eg. mechanical energy) into action potentials
What are the four types of information that describe a sensory stimulus?
- modality
- duration
- intensity
- location
What is modality?
The type of sensation detected or encoded by a sensory nerve eg. light touch, deep pressure, temperature
The PNS can be subdivided into what two nervous systems?
somatic and autonomic nervous systems
The autonomic nervous system can be subdivided into what two divisions?
Sympathetic and parasympathetic nervous systems
We utilise the somatic nervous system to _________ control skeletal muscle
voluntarily
What does the somatic nervous system control?
Voluntary movement of skeletal muscle
We utilise the autonomic nervous system to __________ control internal organs
involuntarily
What does the autonomic nervous system control?
Involuntary regulation of our internal organs via control of smooth and cardiac muscle, and secretory glands
Neurons can be divided into three basic types based on their function. These are:
- afferent (eg. sensory) neurons
- interneurons
- efferent (eg. motor) neurons
Describe the role of afferent (eg. sensory) neurons
To convey information from the tissues and organs of the body to the CNS
Describe the role of interneurons
They are found exclusively in the CNS and they connect with other neurons within the CNS
Describe the role of efferent (eg. motor) neurons
To convey information from the CNS out to the effector cells such as muscle, gland, or other nerve cells
In the somatic efferent pathway, how many neurons are there between the brain and the effector?
2
In the autonomic efferent pathway, how many neurons are there between the brain and the effector?
3
What are the effectors of the somatic efferent pathway?
Skeletal muscle
What are the effectors of the autonomic efferent pathway?
Smooth muscle, cardiac muscle, glands
Within the autonomic efferent pathway, what is the neurotransmitter that is released by the third neuron in the parasympathetic nervous system?
ACh
Within the autonomic efferent pathway, what is the neurotransmitter that is released between the first and second neurons in the sympathetic nervous system?
ACh
Within the autonomic efferent pathway, what is the neurotransmitter that is released by the second and received by the third neurons in the sympathetic nervous system?
ACh
Within the somatic efferent pathway, what is the neurotransmitter that is released between the second neuron and the skeletal muscle?
ACh
Within the autonomic efferent pathway, where is the synapse between the first and second neurons the sympathetic nervous system?
The first synapse is in the brain or spinal cord and the second synapse is very close to the CNS in ganglia
Within the autonomic efferent pathway, where is the synapse between the first and second neurons the parasympathetic nervous system?
The first synapse is in the brain or spinal cord and the second synapse is very distant to the CNS in ganglia, close to the target organ
Within the autonomic efferent pathway, what is the neurotransmitter that is released by the third neuron in the sympathetic nervous system?
NE
Within the somatic efferent pathway, where is the synapse between the second neuron and the skeletal muscle?
Ventral horn of the spinal cord
What is a motor unit?
A motor neuron and all the muscle fibres it innovates
What is the potential with regards to the cell?
The difference in electrical charge between the inside and outside of the cell
Is the inside of the cell relatively negatively or positively charged?
negative
The electrical potential across the cell membrane is
the cell’s membrane potential
Depolarisation induces
excitation
Hyperpolarisation induces
inhibition
