Peripheral nervous system Flashcards
Peripheral nerves of the upper limb- Brachial plexus
Axillary
Musculocutaneous
Radial
Ulnar
Median
Axillary nerve
roots: C5 and C6
muscles innervated: Deltoid and teres minor
sensory functions: skin of the deltoid region/upper arm
Radial nerve
roots: C5-T1
muscles innervated: triceps brachii, brachioradialis, extensor muscles of forearm/wrist
sensory functions: skin of posterior arm and forearm lateral 2/3 of dorsum of hand and fingers over proximal and middle phalanges
Musculocutaneous nerve
roots: C5, 6, 7
muscles innervated: coracobrachialis, biceps brachii, brachialis
sensory functions: lateral half of the anterior forearm and a small lateral portion of the posterior forearm
Lateral cutaneous nerve
roots: L2 and L3
sensory functions: the skin of the anterior half and radial posterior quarter of forearm
Median nerve
roots: C5-T1
muscles innervates: flexor muscles of forearm/ wrist: flexor carpis radialis, palmaris longus, flexor digitorum superficialis, flexor pollicis longus, flexor digitorum profundus
forearm pronators: pronator teres and pronator quadratus
lateral muscles of hand: abductor pollicis brevis, opponens pollicis, flexor pollicis brevis
sensory functions: plamar aspect of hand and fingers, lateral 2/3 (1-3 fingers)
Ulnar nerve
roots: C8 - T1
muscles innervated: flexor carpi ulnaris, flexor digitorum profundus, interossei (palmar and dorsal) lumbricals, adductor pollicis, abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi
sensory functions: skin of medial 1/3 of hand, little finger and medial half of ring finger on both anterior and posterior
Medial cutaneous
roots: C8-T1
sensory functions: skin of medial and posterior aspects of forearm
Peripheral nerves of lower limb- Lumbosacral plexus
Sciatic
Femoral
Obturator
Tibial
Fibular
Sciatic nerve
roots: L4-S3
muscles innervated: hamstrings and adductor magnus
sensory innervation: below the knee
Femoral nerve
roots: L2-L4
muscles innervated: illiacus, rec fem, vastus lateralis, vastus medialis, vastus intermedius, sartorius
sensory: skin over anterior + medial aspect of thigh + medial side of leg + foot
Obturator nerve
roots: L2-L4
muscles innervated: gracilis, adductor longus, adductor brevis, adductor magnus, obturator externus
sensory: skin over medial aspect of thigh
Superficial fibular (peroneal) nerve
roots: L4-S2
muscles innervated: fibularis longus, fibularis brevis
sensory: skin over distal 1/3 anterior aspect of lower leg and dorsum of foot
Deep fibular (peroneal) nerve
roots: L4-S2
muscles innervated: Tibialis anterior, Extensor hallucis longus, Fibularis tertias, Extensor digitorum longus/brevis
sensory: skin on adjacent side of the great toe and second toe
Tibial nerve
roots: L4-S3
muscles innervated: Gastrocnemius, Plantaris, Soleus, Popliteus, Tibialis posterior, Flexor digitorum longus, Flexor hallucis longus
sensory: tibial nerve branches into the medial plantar + lateral plantar nerves in the foot so innervates plantar aspect of foot
Medial and Lateral plantar nerves
roots: L4-S3
medial: abductor hallucis, flexor digitorum brevis, flexor hallucis brevis
sensory: medial 2/3 of plantar aspect of foot
lateral: abductor digiti minimi, adductor hallucis, lumbricals, flexor digiti minimi brevis, interossei (plantar and dorsal)
sensory: skin over lateral 1/3 over plantar aspect of foot
Superior gluteal nerve
roots: L4-S1
branches: superior + inferior branches
muscles innervated: gluteus medius muscle, gluteus minimus muscle, tensor fasciae latae muscle
Inferior gluteal nerve
roots: L5-S2
branches: for gluteus max
muscles innervated: gluteus maximus muscle
Further cutaneous innervation of the lower limb
- Posterior cutaneous nerve of the thigh
- Lateral femoral cutaneous nerve
- Anterior cutaneous nerve
- Sural nerve
1) Olfactory nerve- sensory or motor? function? origin?
sensory
function: nose- smell
originates: cerebrum
2) Optic nerve- sensory or motor? function? origin?
sensory
function: eye- vision
originates: cerebrum
3) Oculomotor- sensory or motor? function? origin?
motor
eyeball + eye lid movements. Lens shape
mid-brain - pontine junction
4) Trochlear- sensory or motor? function? origin?
motor
hearing
mid-brain
5) Trigeminal- sensory or motor? function? origin?
sensory+motor
sensory: face, sinuses, teeth etc.
motor: chewing
brain-stem- Pons
6) Abducens- sensory or motor? function? origin?
motor
eyeball movement + proprioception
pontine-medulla junction
Facial- sensory or motor? function? origin?
motor
facial expressions and sense of taste
pontine- medulla junction
Vestibulocochlear- sensory or motor? function? origin?
sensory
hearing and equilibrium
pontine-medulla junction
Glossopharyngeal
motor and sensory
motor: pharyngeal musculature
sensory: tongue, tonsil, pharynx
medulla oblongata
Vagus- sensory or motor? function? origin?
sensory and motor
heart, lungs, bronchi, GI tract, trachea, larynx
medulla oblongata
Accessory- sensory or motor? function? origin?
motor
shoulder and neck muscle movements
medulla oblongata
Hypoglossal- sensory or motor? function? origin?
motor
ability to move the tongue
medulla oblongata
What information do ascending spinal tracts form?
sensory information up the spinal cord to areas of the brain
What information do descending spinal tracts form?
motor information from the brain to specific levels of the spinal cord
Spinothalamic tract- sensory or motor? function?
sensory
sense pain, itch, temp, crude touch
Corticospinal tract- sensory or motor? function?
motor
primary motor activity
Tectospinal tract- sensory or motor? function?
motor
reflex activity of the head, eyes and trunk in response to stimuli
Spinocerebellar tract- sensory or motor? function?
sensory
unconscious proprioceptive info
Reticular spinal tract- sensory or motor? function?
sensory
postural control (trunk and limbs), preparing movements
Gracile fasciculus- sensory or motor? function?
(lower body)
sensory
vibrations, conscious proprioception + fine touch of lower body
Vestibulospinal tract- sensory or motor? function?
motor
control of gross extensor muscles to maintain balance + posture in response to head movements
Cuneate fasciculus- sensory or motor? function?
(upper body)
sensory
vibration, conscious proprioception + fine touch of the upper limbs
Rubrospinal tract- sensory or motor? function?
motor
large muscle flexion, fine motor control of upper limbs
What is a reflex?
a fast, unplanned sequence of actions that occurs in response to a particular stimulus
What are the 5 functional components of a reflex arc?
- Sensory receptors- responds to a stimulus
- Sensory neuron- along the axon to axon terminals located in grey matter of spinal cord
- Integrating center- grey matter within CNS
- Motor neuron- impulses move out of the CNS to the specific part of the body
- Effector- part of the body that responds to the motor neuron
What are the two fibres that sense pain (nociceptors)
- A delta fibers- send fast signals
- C fibers- send slow signals
What type of pain do A delta fibres cause?
Sharp, stinging pain that is localised? Arises mainly from skin
What type of pain do C fibres cause?
Arises mainly from skin but also tissues and muscles.
It is more diffuse and longer in duration than fast pain
The pain pathway
- Fibers send painful stimuli from the skin (nociceptors) to the peripheral nerve then to the spinal nerve
- Stimulus passes to the sensory dorsal root, via the dorsal root ganglion into the grey matter- which is transferred into white matter tract.
- From the spinothalamic tract, the painful stimulus goes to the thalamus (relay centre) then sent to the somatosensory cortex
How nociceptors transmit pain to the brain
- Transduction- noxious stimuli detected by nociceptors
- Conduction- impulse conducted through DRG nerve fibers to the spinal cords
- Synaptic transmission/ modulation- spinal cord receives nociceptive signals, modulating their amplitude and relaying them up to the brain
- Perceive pain- signals travel to the somatosensory cortex where the pain is recieved
Regeneration
- sprouting of new dendrites
- new protein synthesis
- synaptic changes with other neurons
PNS lesions and repair- when can axons and dendrites repair?
- If cell body is in tact
- Schwann cells need to be remain functional
- Scar tissue formation must not be too quick
PNS lesions- withi 1-2 days following injury…
Nissl bodies break up into granular masses (chromatolysis)
PNS lesions- within 3-5 days following injury…
- the axon distal to the injury swells and breaks up
- the myelin sheath deteriorates
- but neurolemma still remains
- this degeneration is called Wallerian degeneration
PNS lesions- following chromatolysis… (axon rebuidling)
- signs of recovery in the cell body become evident
- macrophages phagocytize the debris
- protein synthesis accelerates
- RNA synthesis accelerates
PNS lesions- after axon rebuilding
- Scwann cells on either side of the injured site multiply by mitosis
- this may form a regeneration tube across the injured area.
- this tube guides growth of a new axon, as long as the gap isn’t too big
Categories of neurological conditions
Intermittents and unpredictable- relapses + remissions lead to marked variation in the care needed
Progressive- where progressive deterioration in neurological function leads to increasing depence on help + others
Stable- but with changing needs due to development or ageing
Neural plasticity
is the CNS ability to adapt to functional demands + re-organize
e.g unmasking of synapses, sprouting of new fibers, cortical re-organization/ re-mapping
How are electrical impulses transmitted down an axon?
they pass through the axon from the neuron- which requires an action potential
What’s a nerve impulse?
diffusion of ions across a cell membrane of the neuron
Resting potential
- when a cell isn’t firing
- negatively charged inside the axon
- 3 sodium ions out for every 2 potassium ions in
How a signal is sent along the axon…
- in response to a signal, the soma end of the axon becomes depolarized
- the depolarization spreads down the axon. meanwhile the first part of the membrain repolarizes because sodium ion channels are inactivated and additional potassium ion channels have opened so cannot depolarize.
- the action potential continues to travel down the axon
Repolarization
- Sodium gates close
- Potassium pumps kick in to repolarize
- Potassium ions rush out of the cell, so cell more negative and ready for next action potential
Hyperpolarization
Can occur when the cell becomes too negative
What is a synapse
a space between the pre-synaptic terminal and the dendrites of the next neuron
What are leak channels
Channels that randomly alternate between open and closed
What are ligand-gated channels
Channels that open and close in response to binding of a ligand/chemical e.g neurotransmitters/hormones
What are mechanically-gated channels
Channels that open and close in response to a mechanical stimuli such as vibration, touch, pressure or tissue-stretching
What are voltage-gated channels
Channels that open in response to change in voltage
Graded potentials- origin? types of channels? conduction? amplitude? duration? polarity? refractory period?
- Arise mainly in dendrites and cell body
- Ligand-gated or mechanically-gated ion channels
- Not propagated; permit communication over short distances
- Depending on strength of stimulus, varies from less than 1mV to more than 50mV
- Typically longer
- May be hyperpolarizing (inhibitory to generation of action potential) or depolarizing (excitatory to generation of action potential)
- Not present; summation can occur
Action potentials- origin? types of channels? conduction? amplitude? duration? polarity? refractory period?
- Arise at trigger zones and propagate along axon
- Voltage-gated channels for sodium ions and potassium ions
- Propagate and thus permit communication over longer distances
- All or none
- Shorter
- Always consist of depolarizing phase followed by repolarizing phase and return to resting membrane potential
- Present; summation cannot occur
Typical chemical synapse event
- nerve impule arrives at a presynaptic cleft
- depolarizing phase of nerve impulse opens voltage gated calcium ion channels
- calcium ions are more concentrated outside the cell, so calcium ions flow in
- increase in calcium ions signals the synaptic vesicles to merge with the cell membrane
- vesicles contain acetylcholine, which is released into the synaptic cleft and diffuses across the synaptic cleft
- Acetylcholine binds with receptors on post-synaptic membrane- which can be excitatory or inhibitory
- depolarizing causes post-synaptic action potential
What is endocytosis?
A process where substances are brought into the cell + form vesicles
What is exocytosis?
Transport of molecules outside the cell
What 2 sub groups can neurotransmitters be divided into?
Small molecule neurotransmitters + neuropeptides
What are the 6 small molecule neurotransmitters?
- Acetylcholine- excitatory and neuromuscluar junctions but inhibitory at other synapses
- Amino acids- glutamate and aspartate are excitatroy, GABA and glycine are inhibitory
- Biogenic amines- dopamine, serotonin, norepinephrine
- ATP- excitatory in PNS and CNS
- Nitric oxide- excitatory in the brain, spinal cord and adrenal glands.
- Carbon monoxide- excitatory in the brain
What are 5 neuropeptides?
- Substance P- found in sensory neurons in spinal cord and brain associated with pain
- Enkephalins- inhibity pain impulses by suppressing substance P.
- Endorphins- inhibits pain by blocking substance P.
- Dynorphins- controls pain and registering emotions
- Hypothalamic releasing and inhibiting hormones- regulates release of hormones from pituitary
What roots does the brachial plexus start and end from?
C5 to T1
What roots does the lumbar plexus start and end from?
T12 to L4
What roots does the sacral plexus start and end from?
S1 to S4 with contributions from L4 and L5
