Module 3: Nerve and Muscle Flashcards
Two parts of nervous system
Central nervous system
Peripheral nervous system
What makes up the CNS? (2)
Brain and spinal cord
What makes up the PNS? (2)
Peripheral nerves
Ganglia
Which cells make up the CNS and PNS? (2)
Neurons and glia
What are neurons specialised for?
Transmission of information
Main function of glial cells
Provide support for neurons
Dendrite functions (2)
Receive input
Send information to cell body
Where are the organelles in an axon?
In the cell body
Cell body function
Sums inputs
Axon function
Carries action potentials
Axon hillock location and function
Where head meets axon
Initiates action potential
Axon terminal function
Release neurotransmitters
Nucleus (CNS)
Group of cell bodies in the CNS
Tract (CNS)
Bundle of axons in the CNS
Grey matter
Group of cell bodies in spinal cord or cerebral cortex
White matter
Bundle of axons in spinal cord or cerebral fluid
Ganglion
Group of cell bodies in the PNS
Nerve
Bundle of axons in the PNS
What are the four neuron components/ zones?
Input zone
Summation zone
Conduction zone
Output zone
Input zone
Dendrites and cell body
Receives chemical signals from other neurons
Summation zone
Axon hillock
Summation of inputs
Conduction zone
Axon
Carries action potentials
Where does the axon carry action potentials between? (4)
Between brain areas
To and form spinal cord
From peripheral sensory receptors
To effector cells
Output zones
Axon terminals
In contact with input zone of effectors or other neurons. Releases neurotransmitters
What is a neurotransmitter a type of?
Chemical signal
Name the four neuron types
Multipolar
Bipolar
Unipolar
Anaxonic
Multipolar neuron
Neuron with multiple processes emanating from cell body
Bipolar neuron
Neuron with two processes emanating from cell body
Unipolar neuron
Neuron with one process emanating from cell body.
This process branches into a dendrite and an axon
Anaxonic neuron
A neuron with no distinct axon. All processes look alike
Five types of glial cells
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
Schwann cells (PNS)
Astrocyte functions (3)
Supply nutrients to neurons
Ensheath blood capillaries
Respond to injury
Microglia function
Engulf microorganisms and debris
Immune cells of the CNS
Ependymal cell function
What special component do they contain?
Line fluid-filled spaces of the brain and spinal cord
Cilia
Oligodendrocyte function
Support axons by ensheathing them with myelin sheath
Schwann cell function
Support peripheral nerve fibres by ensheathing them with myelin
How do Schwann cells ensheath the axon? What tissue is used?
Wrap their plasma membrane around the axon.
Fat (phospholipid)
Which two glial cells are similar in function?
Oligodendrocytes and Schwann cells
What are the gaps between myelin called? What effect do these have?
Nodes of Ranvier
Help to increase conduction
Synapse
A junction where communication between neurons occurs
Where does the axon potential travel to/from?
From axon hillock to axon terminal
What happens after action potential reached axon terminal?
Synaptic vesicles containing neurotransmitter fuse with the membrane and release it into the synaptic cleft
At what point is the neurotransmitter transmitted to the post-synaptic neuron?
At the input zone receptors
How does the signal change during communication between neurons?
Electrical to chemical to electrical
Action potential to neurotransmitter to action potential
Synaptic cleft
Small space between axon terminal of pre-synaptic cell and dendrites of post-synaptic cell
Synaptic vesicle
Vesicle containing neurotransmitter which waits for a signal to release it
What is the cell releasing neurotransmitter called?
Pre-synaptic neuron
What is the cell receiving neurotransmitter called?
Post-synaptic neuron
Afferent information
Information coming into the brain
Efferent information
Response that comes out of the brain
How do we remember the difference between afferent and efferent?
Afferent is information ascending up to the brain
Somatic information
Information we are aware or/ have control over
E.g. voluntary muscle control
Autonomic information
Information we have no awareness of/ body oversees automatically
E.g. blood pressure
Effectors of somatic efferent division
Skeletal muscle fibres
Somatic efferent diversion neurons
Upper motor neuron
Lower motor neuron
Position of upper motor neuron
Cell body in brain
Axon in spinal cord
Position of lower motor neuron
Cell body in spinal cord
Axon in spinal nerve
Similarity between upper and lower motor neurons
Both are myelinated
Where is the first synapse located in somatic efferent division?
In spinal cord
Where is the second synapse located in somatic efferent division?
Between lower motor neuron and skeletal muscle fibres
Which neurotransmitter do somatic efferent division synapses release?
ACh acetylcholine
Two divisions of the autonomic efferent nervous system
Sympathetic and parasympathetic
Effectors of autonomic efferent nervous system (4)
Smooth muscle
Cardiac muscle
Glands
Adipose tissue
How many neurons are used in autonomic efferent pathway?
Three
Positions of neurons in autonomic efferent pathway
- Cell body in brain, axon in brain or spinal cord
- Cell body in brain or spinal cord, axon in PNS
- Cell body and axon in PNS
Are autonomic efferent pathway neurons 2 and 3 myelinated?
2 is, 3 isn’t
Where is the synapse between neurons 2 and 3 in the autonomic efferent pathway?
In an autonomic ganglion
Where is the synapse between neuron 3 and effector in the autonomic efferent pathway?
On effector
How can we refer to neurons about an autonomic ganglion? (2)
Pre-ganglionic neuron
Post-ganglionic neuron
Which neurotransmitter does the first synapse in autonomic efferent pathways release?
Acetylcholine ACh
Which neurotransmitter does the second synapse in autonomic efferent pathways release?
Acetylcholine ACh in parasympathetic division
Norepinephrine NE/ nonadrenaline
Which system does the term ‘fight or flight’ refer to?
Sympathetic division
Which division does the term ‘test and digest’ refer to?
Parasympathetic
Which factors increase and decrease in the sympathetic division?
Increase: heart rate, pupil size, sweating
Decrease: gastric motility, salivation
Which factors increase and decrease in the parasympathetic division?
Decrease: heart rate, pupil size, sweating
Increase: gastric motility, salivation
In which levels of the spinal cord do cell bodies of sympathetic neurons (second) lie?
Thoracolumbar levels
T1-L2
In which spinal cord levels do the cell bodies of parasympathetic neurons (second) lie?
Cranial and sacral levels
Where so sympathetic ganglia lie?
On either side of vertebral column
Where do parasympathetic ganglia lie?
Synapse in or near effector
Which division has a short second axon?
Sympathetic
Which division has a long second axon?
Parasympathetic
Membrane potential
Distribution of ions inside and outside the cell which creates a difference in charge across the membrane
Resting membrane potential
-70mV
Mechanisms maintaining resting potential (2)
Leak channels (potassium and sodium)
Voltage gated channels (potassium and sodium)
What lies at the initial segment of the axon?
High concentration of sodium channels
Where is it decided if AP propagation will go ahead or not?
Axon initial segment
Gates of ion channels (2) and when they open and close
Activation gate: opens when action potential arrives (closer before)
Inactivation gate: closes after depolarisation (open before)
Step one of action potential (at threshold)
A local change in membrane potential occurs sufficient to depolarise the cell
Na+ channels open
Step two of AP
Na+ channels are open and slow Na+ into the cell
Depolarisation occurs
Step three of AP
Na+ channels close
K+ channels open
Repolarisation occurs
Step 4 of AP
K+ channels close
Membrane hyperpolarises because K+ channels are slower to close.
Potential returns to resting and both channels close
Absolute refractory period
Interval of time in which a second action potential absolutely cannot be initiated
Occurs during depolarisation and repolarisation (steps 2 and 3)
Relative refractory period
Interval of time in which a second AP can be generated, but it requires a much larger stimulus than the first AP.
Occurs during hyperpolarisation (step 4)
Propagation of action potentials
A regeneration of action potentials along the axon
How do AP propagation and conduction of electricity differ?
APs are regenerated, not conducted. New versions of the same signal are produced- the same one isn’t carried the whole way down the axon
Describe AP propagation
Generated at initial segment and sodium channels open there.
Action potential develops in segment 2. Initial segment begins repolarisation by opening potassium channels.
A headed depolarisation brings segment 3 membrane to threshold.
Why can APs only move forward?
Because the initial segment membrane goes into the absolute refractory period of repolarisation
How does propagation of AP in unmyelinated axons differ from that in myelinated axons?
AP jumps from node to node in myelinated axons. The internodes (Schwann cells) act as excellent conductors.
A stimulus at resting potential produces ____?
A graded potential
A graded potential may generate ____?
An action potential
An action potential triggers _____?
Synaptic activity
Synaptic activity leads to _____?
Information processing
Where does ACh bind to on the post-synaptic neuron?
Protein channels in membrane
Event one of transmission at synapse
Action potential triggers opening of voltage-gated channels
What occurs after action potential triggers opening of channels?
Calcium ions diffuse into the axon terminal and trigger synaptic vesicles to release ACh
What occurs after synaptic vesicles release ACh?
ACh diffuses across the synaptic cleft and bonds to voltage-gated channels
Producing a graded depolarisation (or EPSP)
EPSP
Excitatory post synaptic potential
What ends depolarisation/ EPSP?
AChE breaking down ACh into acetate and choline
What happens to the choline that is produced from breaking down ACh?
The axon terminal reabsorbs it from the synaptic cleft and uses it to synthesise new ACh
IPSP
Inhibitory post synaptic potential
Is there summation at an NMJ?
No- NMJ synaptic transmission is excitatory and absolute
Temporal summation
Summation over time
Secondary action potentials build on initial one
Spatial summation
Summation in space
Two simultaneous stimuli from two different neurons summate to give large action potential
Where does the spinal cord start?
Foremen magnum (opening at base of skull)
Where does the spinal cord end?
Inferior border of L1
Where does the spinal cord lie?
Within a meningeal sac that fits within the spinal cavity
CSF
Cerebrospinal fluid
Where is the CSF in the spinal cord?
Filling the meningeal sac
Purpose of CSF in spinal cord
Act as gel cushion for spinal cord
Conus medularis
Non-neural tissue which attached filium terminale
Filium terminale
Fibrous non-neural tissue which anchors the spinal cord to the coccygeal vertebrae
How many segments of spinal nerves are there?
31
How many segments of spinal nerves in the cervical part are there?
8
Cauda equina
The group of spinal nerves which have to descend from L1 to their exit vertebrae
Dorsal/ posterior column
Region of white matter in the spinal cord which lies between the dorsa horn and the posterior median sulcus
Ventral column
Region of white matter in the spinal cord which lies between the ventral horn and the ventral median fissure
Lateral column
Region of white matter in the spinal cord which lies between the ventral and dorsal columns
Doral median sulcus
Central furrow in posterior region of spinal cord
Ventral median fissure
Deep sulcus (furrow) in the anterior region of the spinal cord
Central canal
Canal in centre of spinal cord
Three horns of grey matter in the spinal cord
Dorsal lateral and ventral horns
Which section of the spinal cord is associated with efferent division?
Ventral- information moves out
Which section of the spinal cord is associated with the afferent division?
Dorsal- sensory, information moves into spinal cord
What does damage to the dorsal section of the spinal cord cause?
Paralysis of muscles- somatic motor neurons can’t function
What does damage to the ventral section of the spinal cord cause?
Loss of sensation- sensory neurons affected
Where do somatic motor neurons lie in the spinal cord? Is it their axons or cell bodies?
Ventral horn
Cell bodies
Where do autonomic motor neurons lie in the spinal cord? Is it their cell bodies or axons?
Lateral horn
Cell bodies
Where do motor commands leave the spinal cord from?
Ventral nerve root
Where in the spinal cord do the cell bodies and axons of sensory neurons lie?
Cell bodies in dorsal root ganglion
Axons in dorsal nerve root
How does sensory information enter the spinal cord?
Through the dorsal nerve root
Dorsal nerves carry _____ information?
Afferent
Ventral nerves carry _____ information?
Efferent
Three branches from spinal nerve
Dorsal ramus
Anterior ramus
Rami communicantes
Dorsal ramus innervates ___?
The back
Ventral ramus innervates ___?
The front and limbs
Which spinal nerves are rami communicantes present in?
T1-L2
Which kind of axons do rami communicantes contain?
Autonomic sympathetic
Layer covering axon
Endoneurium
Axons bundle to form ____?
Fasicle
Fasicle is covered with _____? (Neural)
Perineurium
Fasicles are bundled with ____ to form a ____? (Neural)
Blood vessels
Nerve
Layer covering a nerve
Epineurium
Three layers of the meninges
Dura mater
Arachnoid layer
Pia mater
Outermost layer of the meninges
Dura mater
Function of dura mater
Dense and fibrous- acts as first line of defence for the brain of cranium fractures
How many layers does the dura mater have?
Two- outer and inner
Space between two dura mater layers where they split
Venous sinuses
What forms the dura folds?
Inner layer of dura mater
Three features of the dural folds
Formed from inner layer of dura mater
Separate major divisions of the brain
Provide stability of the brain within the cranium
Three dural folds
Falx cerebri (big sickle) Falx cerebelli (smaller sickle) Tentorium cerebelli (tent)
Where does the falx cerebri sit?
Between cerebrum in median/ sagittal plane
Where does the falx cerebelli sit?
Between cerebelli hemispheres in the sagittal/ median plane (below falx cerebri)
Where does the tentorium cerebelli lie?
Separating the cerebrum from the cerebellum in the horizontal plane
Three features of venous sinus
Located where the two layers of dura mater separate
Collecting veins
Collecting venous blood from the brain and old CSF from the ventricular system
Venous blood
Deoxygenated blood
Which is the ‘spider-like’ layer and why is it called this?
Arachnoid layer
Sits up on ‘legs’ and has a webbed pattern
Five features of arachnoid
Beneath dura mater
Above Pia mater
Contains subarachnoid space and arachnoid granulation a
Contains blood vessels within subarachnoid space
Does not extend into sulci (like Pia)
Where is the subarachnoid space and what fills it?
Between arachnoid and Pia mater
CSF
Function of arachnoid granulations
Perforate the inner layer of dura mater to transport old CSF from subarachnoid space into the venous sinus
Four features of Pia mater
Inner layer of the meninges
Transparent and delicate
Provides cushion for blood vessels in arachnoid
Adheres to brain and follows gyri- extends into sulci
Four features of the ventricular system
Network of interconnected ventricles within the brain
Filled with CSF (nourishes and protects brain)
Ependymal cells lining the ventricles, circulating CSF
CSF is produced by choroid plexus
Ventricles (5)
2 lateral ventricles (one in each cerebral hemisphere)
Third ventricle (in the diencephalon)
Central aqueduct (midbrain)
Fourth ventricle (level with cerebellum)
(Also central canal)
How does CSF circulate the ventricle system and what are its two main purposes?
Lateral ventricles to third ventricle to cerebral aqueduct to fourth ventricle to subarachnoid space
Then it flows around the brain and spinal cord in the subarachnoid space
Ends in venous sinuses (through arachnoid granulations)
Name the lobes of the brain (4)
Frontal
Parietal
Occipital
Temporal
Which sulcus separates the frontal and parietal lobes?
Central sulcus
Which sulcus separates the parietal and occipital lobes?
Parietal-occipital sulcus
Which sulcus separates the temporal lobe from the frontal and parietal lobes?
Lateral sulcus
Which fissure separates the cerebrum from the cerebellum? What structure fits in this fissure?
Transverse fissure Tentorium cerebelli (a dural fold)
Function of frontal lobe (2)
Motor control
Somatosensory in the anterior part
Function of parietal lobe
Somatosensory
Function of occipital lobe
Vision
Functions of temporal lobe (2)
Memory
Hearing
Name the seven internal structures of the brain
Cerebral cortex Corpus callosum Diencephalon Cerebellum Midbrain Pons Medulla oblongata
Two parts of the diencephalon
Thalamus and hypothalamus
Three parts of the brain stem
Midbrain
Pons
Medulla oblongata
Most superior internal structure of the brain
Cerebral cortex
Most inferior structure of the brain
Brain stem (medulla oblongata)
Three types of white matter in the brain
Commissural tracts
Projection tracts
Association tracts
Commissural tracts
White matter in which axons cross sides of the brain
Projection tracts
Whyte matter in which axons extend from the cortex into other areas of the CNS
Association tracts
White matter in which axons extend to another area in the brain on the same side
Allows for communication between brain areas
Deep nuclei
Are they darker or lighter?
Structures in the brain containing cell bodies
Darker
Gyri next to central sulcus (2)
Precentral gyrus
Postcentral gyrus
Pre-central gyrus
Gyrus of motor cortex next to the central sulcus
Post-central gyrus
Gyrus of the somatosensory cortex next to the central sulcus
Corticospinal pathway
Two neurons between brain and effector
Describe neurons of the corticospinal pathway
Upper motor neuron:
- cell body in precentral gyrus (primary motor cortex)
- axon extends to spinal cord on opposite side
- synapses on lower motor neuron
Lower motor neuron:
- cell body in ventral horn of spinal cord
- axon extends out of ventral root into PNS
- synapses on skeletal muscle
Dorsal/ posterior column pathway
Three neurons between sensory receptors and somatosensory neuron in postcentral gyrus
Describe the neurons in the dorsal/ posterior column pathway
Neuron 1: (unipolar)
- cell body in dorsal root ganglion
- peripheral fibre from sensory receptors in skin
- central fibre ascends in dorsal columns
- synapses on neuron 2 in medulla oblongata
Neuron 2:
- cell body in medulla oblongata
- axon crosses to opposite side of spinal cord and ascends
- synapses on neuron 3 in thalamus
Neuron 3:
- cell body in thalamus
- axon ascends to somatosensory cortex
- synapses on cell body of somatosensory cortex neuron
What will damage to the primary motor cortex cause?
Paralysis and muscle weakness for the corresponding area on the opposite side of the body
What will damage to the primary somatosensory cortex cause?
Loss of sensation/ no perception of touch in the corresponding area on opposite side of the body
Because information has nowhere to go
Describe five steps of the reflex arc
- Stimulation of receptor
- Activation of sensory neuron
- Information processing in the CNS
- Activation of motor neuron
- Response of peripheral effector
Spinal reflex
Name two types
An automatic response to a particular stimulus
Stretch
Withdrawal
Stretch reflex
A spinal reflex that regulates muscle length through stimulation of the muscle spindle
What surrounds the muscle spindle?
Muscle fibres
How many synapses in the stretch reflex?
One- between sensory and motor neurons
Withdrawal reflex
Spinal reflex which protects the body from damaging stimuli
How many synapses in the withdrawal reflex?
Two: sensory neuron to inter neuron
Interneuron to motor neuron
What is the role of the interneuron in the withdrawal reflex?
Converts the excitatory input from the sensory neuron into inhibitory input into motor neuron on extensor muscles
While relaying excitatory input onto motor neuron on contracting muscle
Role of muscle spindle
Regulate length of muscle fibres
How is work distributed over a muscle?
Each motor unit relaxes while others are stimulated, before it is recruited again
Which three regions of the brain are involved in preparation for movement?
Frontal lobes
Premotor cortex
Cerebellum
Main function of cerebellum
Prepares and performs movement
How does the cerebellum assist movement? (4)
Coordinates muscles- guided by sensory feedback
Compares intended movement with actual result
Helps maintain posture and gaze
Helps learn and automate movements
What causes ‘drunken gait’?
Damage to the cerebellum
What shape are sensory neurons?
Unipolar
Where does sensory input enter the axon?
Dendrites
5 special senses
Vision Hearing Taste Smell (pheromones) Vestibular (balance)
4 somatic & visceral sensations
Touch
Pain
Warm and cold
Body position
Role of sensory receptor
Transduces information to neuron by converting physical energy into AP
How can we describe a sensory stimulus (4)
Modality
Intensity
Duration
Location
Modality
Type of sensory receptor activated
Intensity (sensory information)
Frequency of action potential firing in afferent neuron
Duration (sensory information)
Duration of action potential in firing afferent neuron
Location (sensory information)
Location of sensory receptor(s) activated, mapped in the brain
Is there a sensory receptor on a muscle spindle?
No. The axon of the sensory neuron wraps around the spindle
Receptive field
Region of space on the body surface in which a stimulus can lead to activity in a particular afferent neuron
What will activate more than one receptive field?
A stronger stimuli
What does a small receptive field provide?
Good discrimination between stimuli
‘labelled line’
Label on the sensory axon saying where the ap has come from
Function of somatic sensory association cortex
Generates conscious sensation from action potentials
Sensation vs perception
Sensation is conscious identification of what and where. Occurs in primary region of somatosensory cortex.
Perception is meaningful interpretation of the sensation. Occurs in the association region of the somatosensory cortex
Do densely innervated areas of the body occupy small or large regions of the somatosensory cortex?
Large regions
