Week 2 - Neuromuscular

CNS - components (2)

brain and spinal chord

PNS - components

nerves connecting the central nervous system to the body

Includes neuronal clusters (ganglia) at specific locations along peripheral nerves

Naming of human head positions

Humans rostro-caudal = towards nose and tail bone -> back and front = dorsal and ventral

CNS of humans has a 90° bend because of cephalic flexure -> anything above the midline of the head has different names

cells of CNS - list (4)

can be loosely categorised into neurons (functional units) or glial cells

Astrocyte -> important components of synaptic transmission and in blood brain barrier

Microglia -> type of immune cell that plays surveillance role for dyeing cells or infections

Oligodendrocyte -> form myelin that insulates axons so action potentials can travel faster

Neuron -> functional cells

major regions of CNS - list (4)

• Cerebrum

• Diencephalon -> hypothalamus, thalamus, pineal gland (part of epithalamus)

• Brainstem -> mid brain, pons, medulla, oblongata

• Cerebellum

major folds of brain - list (4)

Longitudinal fissure separates left and right hemisphere

Central sulcus essentially divides brain into front and back bit (somewhat midline) -> can be followed from longitudinal fissure to down laterally

Parietal-occipital sulcus = separates parietal and occipital lobes

Transverse fissure defines location of temporal lobe

major folds of brain - pre and post central sulcus

Postcentral gyrus = after central sulcus -> location of primary sensory cortex

• All sensory info ends up in postcentral gyrus

Precentral gyrus = before central sulcus -> location of primary motor cortex

• Ability to move muscles comes from neurons in precentral gyrus

folds of cerebellum

undulations called folia instead of gyri like in rest of brain → looks like patterns on leaves

role of insular cortex

important part of limbic nervous system → emotions

role of corpus callosum

composed of axons that allow for communication between left and right hemispheres

Grey and white matter (2 grey 1 white)

Grey matter cortex = location of cell bodies of neurons -> not myelinated

Grey matter nuclei (basal ganglia or basal ganglia) -> pockets of grey matter deeper in the brain

• Location of where electrodes would be placed to treat someone with Parkinsons

White matter = composed of myelinated axons

• Oligodendrocytes (glial cells) provide insulation to nerve axons and gives them a white appearance

layers protecting the brain - list (4)

1. Skin of scalp

2. Periosteum -> lines bone

3. Bone of skill

4. Meninges and cerebral spinal fluid

meninges and spaces in-between- list (5)

1. dura mater

2. subdural space

3. arachnoid mater

4. subarachnoid space

5. pia mater

meninges and spaces in-between - dura mater (3)

Directly under skull

Very thick, tough, fibrous structure

Different folds of the dura mater sit within fissures of the brain

meninges and spaces in-between - folds of dura mater (3)

• Falx cerebri = dural fold that sits in longitudinal fissure -> separates hemispheres and provides protection

• Tentorium cerebelli = dural fold that sits in space between cerebellum and cerebrum (transverse sinus)

• Falx cerebelli = dural fold that sits between hemispheres of cerebellum

meninges and spaces in-between - importance of subdural space

Dura mater is associated with lots of blood vessels -> if one were to rupture, blood would spill into the subdural space (subdural bleed)

Because dura mater does not expand, pressure forms on brain

meninges and spaces in-between - subarachnoid space

location of CSF

meninges and spaces in-between - pia mater

Very think and fine membrane that sits on surface of brain → hard to separate from brain

superior saggital sinus - summary

large blood vessel within dura mater

Arachnoid villus protrudes from arachnoid mater into superior sagittal sinus → important for reabsorption of CSF into vasculature

production and re-absorption of CSF - steps (4)

1. Blood flows into choroid plexus ->  specialised capillary bed in vascular tissue

2. When capillary bed fills with blood, some of the plasma can be filtered via gaps between endothelial cells into the ventricles to form CSF

3. As ventricles fill, CSF eventually finds its way out into the subarachnoid space to bathe the brain

4. As CSF enters into arachnoid villi (granulations) and pressure increases, CSF is forced back into blood circulation

CSF - def

fluid filtrate from blood that bathes the brain and protects it by providing cushioning

Production occurs within ventricular system of central nervous system

consequence of CSF not being reabsorbed in adults

increase in pressure in subarachnoid space -> pressure exerted onto neural tissue -> widespread neurological problems

consequence of CSF not being reabsorbed in children - born without arachnoid granulations (4)

Results in condition called hydrocephalus (water on brain)

In children, sutures of the skull are not fused yet -> skull can expand resulting in an enlarged head

Treated by catheter inserted into lateral ventricles that drains CSF from ventricles into another vascular bed

Drainage tube usually introduced into peritoneal cavity with extra length to allow for growth of child

organisation of cerebral cortex

most primary cortices are located around deepest sulci/ fissures

• Central sulcus -> surrounded by primary somatomotor and somatosensory cortices

• Lateral fissure -> surrounded by primary auditory and gustatory cortices

• Calcarine sulcus -> surrounded by primary visual cortex

brainstem - location

between diencephalon and spinal chord

brainstem - major divisions (3)

1. Midbrain -> mesencephalon

2. Pons -> "the bridge" between the rest of the brain stem and the cerebrum and cerebellum

3. Medulla oblonga -> myelencephalon = bulbus

protection of spinal chord

Meninges and CSF in sub-arachnoid space protect the spinal chord as well as the brain

spinal chord segments - list (5)

1. cervical

2. thoracic

3. lumbar

4. sacral

5. cocygeal

enlargement of spinal chord segments (4)

Cervical and lumbar portions are enlarged compared to thoracic portion → have nerves that extend into limbs 

more cells in that area = increased diameter of chord

Cervical = nerves to upper limbs

lumbar = nerves to lower limbs

end of spinal chord

ends at L2

structure called conus medullaris

end of spinal chord - cauda equina (3)

Nerves extend down within the vertebral column and exit at each vertebral level until one single fibre is left (filum terminale) -> attaches to coccyx

Filum terminale is not a nerve but an extension of the pia mater

Bundle of nerves that extend down = cauda equina

spinal cord development - process (3)

1. First trimester: spinal chord fills enter vertebral column

2. later in embryonic development: chord starts to creep up vertical colum until it gets to around L2 → muscoskeletal growth occurs at faster rate than elongation of spinal cord

3. nerves that give rise to peripheral nerves that go into tissues stretch to accomodate and elong with vertebral coumn → forms cauda equina

spinal cord - lumbar puncture (2)

collection of CSF from thecal sac that surrounds spinal chord

Because spinal chord ends around L2, safer to collect CSF from subarachnoid space just below level of Conus medullaris -> between L3 and L4 without damaging spinal chord

grey and white matter of spinal chord

Grey matter found deeper within white matter of spinal chord -> arranged in butterfly shapes

grey and white matter of spinal chord - grey matter components (3)

• Posterior (dorsal) horn = horn on posterior surface

• Anterior horn = horn on ventral surface

• Lateral horn = sticks out on lateral aspects

grey and white matter of spinal chord - white matter components (3)

• Posterior funiculus

• Lateral funiculus

• Anterior funiculus

grey and white matter of spinal chord - white matter arrangement (3)

• Efferent pathways = descending

• Afferent pathways = ascending

nerves - def and structure (3)

collections of nerve fibres (axons) within external connective tissue sheath (epineurium)

Axons grouped into fascicles within nerves and surrounded by perineurial sheath → can be either sensory or motor axons

Each nerve fibre surrounded by endoneurium

types of nerves (2)

• Spinal nerves = nerves that arise from the spinal cord

• Cranial nerves = nerves that arise from the brain or brain stem

spinal cord - location of neuron cell body

cell body of motor neurons = found within boundaries of CNS

cell body of sensory neurons = just outside boundary

PNS - types of neurons (2)

Sensory (afferent) neurons = periphery neurons that carry signals to the CNS

Motor (efferent) neurons = peripheral neurons that carry signals from the CNS

connection of neurons to CNS (3)

Separate spinal roots connect efferent and afferent neurons to the CNS

• Ventral surface of spinal chord = axons of motor nerves -> ventral root

• Dorsal surface of spinal chord = axons of sensory nerves -> dorsal root

Ventral horn contains ventral root -> dorsal horn contains dorsal root

Dorsal root ganglia = cell body of sensory neurons and their axons -> extend into the periphery and into dorsal horn of grey matter in spinal chord

spinal reflex - steps (5)

1. Sensory receptor

2. Sensory neuron

3. Interneuron

4. Motor neuron

5. Effector organ

pairings of spinal nerves - list (31)

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

number of vertebral bones to spinal nerve pairings

30 bones → 31 spinal nerve pairs

Cervical nerve 1 arises above vertebral bone C1 etc → cervical nerve 8 arises below vertebral bone C7

 T1 is below the T1 vertebra etc

branching of dorsal and ventral roots

form spinal nerves → branch into dorsal or ventrla ramus

rami - def

branches of mixed spinal nerve -> contain both sensory and motor axons in contrast to dorsal and ventral root

dorsal and ventral rami

Dorsal ramus wraps around back of body to innovate all muscle and skin on posterior side of anatomy

Ventral ramus wraps around front of body to innovate all anterior structures

segmental innervation - def

concept that each spinal segment have a spinal nerve associated with it will have a distinct dermatome and a distinct myotome

Each spinal nerve will innovate a very defined region of the body -> each of the nerves that is part of the cord will have a very define pattern of innovation

clinical importance of segmental innervation

To identify levels of functional deficits due to nerve damage

segmental innervation - dermatome meaning and face

area of skin that is mainly supplied by a single spinal nerve

Face doesn’t have spinal dermatome -> nerves supplied by cranial nerves

No C1 dermatome as it innovates the meninges and other structures excluding the skin

segmental innervation - myotome

group of muscles that a single spinal nerve innervates

cranial nerves - mnemonic

Oh, Oh, Oh, To Touch And Feel Very Glossy Velvet, Ah

cranial nerves - cerebral hemisphere (2)

1. Olfactory

   • Primary sensory nerve for smell

2. Optic

   • Primary sensory nerve for vision

cranial nerves - midbrain (2)

1. Oculomotor

   • Eye movement (not vision)

2. Trochlear

   • Eye movement

cranial nerves - pons (4)

1. Trigeminal

   • Major sensory nerve for face (cranial nerve dermatome)

2. Abducens

   • Eye movement

3. Facial

   • Facial muscle control  -> facial expression

4. Vestibulo-cochlear -> part of both pons and medulla

   • Nerve goes to inner ear for balance and hearing

cranial nerves - medulla (5)

1. Vestibulo-cochlear -> part of both pons and medulla 

2. Glossopharyngeal

   • Sensory innovation to tongue for taste and to pharynx for other sensations like pain

3. Vagus

   • Major parasympathetic nerve

   • Innovates all internal organs and parts of gastrointestinal systems

4. Accessory

   • Innovates things in the neck like muscles

5. Hypoglossal

   • Movement of tongue

cranial nerves - sensory, motor or both

Not all nerves are mixed -> some are purely motor whilst others purely sensory

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somatic nervous system - def

controls voluntary movement of muscles and innovates skin in terms of sensory component

autonomic nervous system - def

effector system in CNS and PNS mediating unconscious homeostatic control of organ and body physiology

Can be divided into parasympathetic and sympathetic

somatic vs autonomic nervous system

somatic = voluntary

autonomic = involuntary

both contain efferent and afferent neurons

somatic motor neurons - location of cell body summary (1)

cell bodies in ventral horn of spinal cord give rise to axons that project to muscle

somatic motor pathway (2)

1. Pre-ganglionic neurons arise from anterior root with cell bodies in anterior column

2. Axons extend down peripheral or anterior ramus

autonomic neural pathway - summary

often has two neurons in the pathway

1. Neuron that resides in spinal chord (pre-ganglionic neuron) projects out

2. pre-ganglionic neuron synapses to a second neuron (post-ganglion neuron) in the chain before controlling tissue of interest

true for parasympathetic and mostly true for sympathetic (sympathetic nervous system also uses hormones like those from the adrenal gland)

autonomic neural pathway - ganglion

Connection between the neurons happens in the ganglion -> collections of cell bodies of the autonomic nervous system

autonomic system - axon length of parasympathetic vs sympathetic

Parasympathetic: pre-ganglion neuron has really long axon because ganglion is located in or very near target tissue

Sympathetic: pre-ganglion neuron has short axon because ganglion sits right next to spinal chord -> post-ganglion neuron has very long axon to reach tissue

autonomic nervous system - thoracolumbar outflow and craniosacral outflow

Sympathetic autonomic nervous system: pre-ganglionic neurons arise from either the thoracic or lumbar parts of the spinal chord

Parasympathetic autonomic nervous system: pre-ganglionic neurons arise form cranial nerves or sacral nerves within spinal chord

division of autonomic nervous system based on origin from spinal chord

thoracolumbar outflow or craniosacral outflow depending on where they arise from

sympathetic autonomic motor pathway - steps (5)

1. Pre-ganglionic neurons arise from lateral horn rather than ventral horn

2. Pre-ganglionic neuron exits spinal chord via ventral roots into mixed spinal nerve

3. Pre-ganglionic neuron enters sympathetic ganglion via white ramus rather than continuing like somatic motor pathway

4. Pre-ganglionic neuron synapses with post-ganglionic neuron in ganglion

5. Post-ganglionic neuron leaves via grey ramus to re-enter into mixed spinal nerve and heads towards target tissue

coordination of sympathetic responses

can be integrated up and down ganglia for coordinated effect

Eg. allows heart rate, gastrointestinal activity and blood pressure to change all at once

pre- and post-ganglionic neurons - white or grey

white ramus because pre-ganglionic neurons are myelinated

grey ramus because post-ganglionic neurons are unmyelinated

parasympathetic autonomic motor pathway - steps (5)

1. Pre-ganglionic neurons arise from lateral horn rather than ventral horn -> cell body in lateral horn

2. Pre-ganglionic neuron exits spinal chord via ventral roots into mixed spinal nerve

3. Pre-ganglionic neuron extends to the target tissue

4. At target tissue, pre-ganglionic neuron synapses with post-ganglionic neuron

5. Post-ganglionic neuron extends to target tissue -> axon is considerably shorter than pre-ganglionic neuron

parasympathetic cranial nerves - list (4)

3. Oculomotor nerve -> narrows pupil and focuses lens

7. Facial nerve -> tear, nasal, salivary gland

9. Glossopharyngeal nerve -> parotid salivary gland

10. Vagus nerve -> viscera as far as proximal half of colon, cardiac, pulmonary and oesophageal plexus

gated ion channel - def

transmembrane protein that can open and close in response to stimulus

Voltage gated ion channel - def

a channel whose open or closed state depends on the value (polarity) of membrane potential

voltage gated ion channel - cause of conformational change (3)

has positively charged amino acids on voltage sensor → attracted to negative charge of intracellular membrane and closed

when cell accumulates positive charged inside cell → protein sensor repelled causing conformational change to open configuration

allows ion flux and change in cell activity

voltage gated ion channels on action potentials (3)

Action potentials depend on presence of voltage gated ion channels in cell membrane -> open and close in response to changes in membrane potential

When membrane potential achieves threshold potential -> voltage gated channels open and close

At fixed membrane potentials (below threshold potential) -> voltage gated channels are open

restriction of voltage-gated ion channels on neurons

restricted to:

1. Axon hillock

2. Axon

3. Axon terminals

Action potentials can only occur if voltage gated ion channels are present

voltage gated ion channels responsible for action potentials (2)

Na+ and K+

Ca2+ = responsible for neurotransmitter release

voltage gated sodium ion channels during action potential - summary phases (3)

1. Resting state: voltage sensing amino acids attracted to negative charge on intracellular side of membrane -> closed

2. Depolarisation (threshold potential): voltage sensing amino acids repelled by accumulating positive charge in intracellular space -> change in conformation to open configuration

3. Refractory period: channel-inactivating segment blocks further influx of Na+

conductance states of voltage gated Na+ channels (3)

1. Closed at resting potential -> capable of opening, low conductance

2. Open from threshold to peak potential -> rapid opening, high conductance

3. Inactive from peak to resting potential -> slow closing triggered tat threshold, not capable of opening due to inactivation gate blocking channel

refractory period of voltage gated Na+ channels

when channel is unable to open again -> must close before they reopen

conductance states of voltage gated K+ channels (2)

1. Closed at resting potential to peak potential -> opening triggered at threshold but opening is slow

2. Open from peak potential through to after hyperpolarisation -> slow closing

type of feedback cycle for action potential

positive

Opening of some voltage-gated Na+ channels triggers influx of Na+ which further decreases membrane potential -> triggers more channels to open

Once membrane reaches threshold potential, action potential automatically generated

action potential - self-regenerating steps (4)

1. Initiated in one segment

2. Depolarisation travel to next segment of axon

3. Threshold in adjacent segment achieved

4. New action potential in adjacent segment initiated

factors affected membrane potential - list (3)

• Opening of ligand gated ion channel on binding of an excitatory neurotransmitter

• Opening of ligand-gated ion channel on binding of an inhibitory neurotransmitter

• Activation of a stretch/ mechanoreceptor

features of action potentials - list (8)

1. All or nothing -> no summation

2. Driven by voltage-gated ion channels

3. Self-renewing

4. Travel the entire length of the axon without diminishment

5. High fidelity

6. Hyperpolarising the membrane will decrease the probability that threshold will be achieved

7. Depolarising the membrane will increase the probability that threshold will be achieved

8. Under normal physiological conditions action potential only initiate at the trigger zone

action potential steps - summary (5)

1. rest

2. depolarisation

3. repolarisation

4. hyperpolarization

5. refractory period

action potential steps - rest (2)

Cell membrane at rest is x75 times more permeable to K+ than Na+ -> due to presence of K+ leak channels on cell membrane

Voltage gated sodium and potassium ion channels closed

action potential steps - depolarisation (2)

Voltage gated Na+ channels open -> membrane very permeable to Na+ and Na+ enters cell, increasing intracellular membrane potential

Voltage gated K+ channels remain closed

action potential steps - repolarisation (2)

Voltage gated Na+ channels become inactive (close) -> Na+ can no longer enter cell

• Rapid fall in Na+ conductance

Voltage gated K+ channels open and membrane becomes very permeable to K+ -> K+ leaves cell and membrane potential falls

• Slow rise in K= conductance

action potential steps - hyperpolarisation (3)

Voltage gated Na+ channels remain closed

Voltage gated K+ channels remain open -> membrane even more permeable to K+ that it would be at rest

Fall in membrane potential overshoots and membrane potential becomes even more negative than RMP

action potential steps - refractory period summary (2)

During and immediately after an action potential -> periods when it is hard to generate new action potentials

Voltage gated ion channels unable to generate another action potential

types of refractory period - list (2)

absolute

relative

absolute refractory period

corresponds to time when voltage-gated sodium channels open or inactive -> needs to close before opening again

relative refractory period

another action potential can be generated because sodium channels have closed but open state of potassium channels makes it relatively harder to reach threshold potential

requires stronger stimulus

graded potentials - def

any change in membrane potential below the threshold potential

occur because gated ion channels are opened or close

occur only at position along emmbrane where gated ion channel was opened

postsynaptic potential - def

graded potential that occurs as a result of synaptic activity

is movement of graded potential along a membrane passive or active

passive

amplitude of change to membrane potential decreases as it travels along axon

excitatory post-synaptic potential (EPSP) - def (3)

type of graded potential

Movement of ions across cell membrane at synapse that depolarises membrane

membrane potential moves closer to threshold