Peripheral Nerves Flashcards
Chain of peripheral nerve function
Sensory nerve receptors - eg, skin, joints, muscles and tendons
Along peripheral nerve
Brain and spinal cord- integration. Spinal cord takes info up to sensory cortex in front of parietal lobe. Info processed to make motor output in motor cortex. Stimulates descending pathways
Through spinal cord
Muscular system- to produce response
2 nervous systems
CNS
PNS
What is in the CNS?
Brain and spinal cord
Brain = receives and processes sensory info, produces responses + stores memories, thoughts and emotions
Spinal cord= conduct signals to and from the brain + control reflexes
Peripheral nervous system
Sensory neurones - pick up sensory info from receptors to spinal cord + CNS
Motor neurones- take info away from spinal cord to muscles or glands
Either somatic (voluntary) or autonomic (involuntary)
Autonomic is sympathetic fight and flight or parasympathetic rest and digest
Types of motor neurones
LOWER MOTOR NEURONES- Neurones with cell bodies in spinal cord or brain stem and axons innervated skeletal muscle
They are peripheral
UPPER MOTOR NEURONES- Transmit signals from brain to lower motor neurones or interneurones in brain stem + spinal cord.
CNS nerves
What two types of nerve in PNS.
Sensory nerves
Motor nerves
Sciatic nerve
Comes from L4-S3,
Along lumbosacral plexus
Exits pelvis via greater sciatic foramen
Gluteal region deep to biceps femoris in Lower thigh
Gives off branches to semitendinosus, semimembranosus, biceps femoris and adductor magnus
Upper limb has brachial plexus with sensory and motor neurones in a bundle which are peripheral nerves
What are cranial nerves?
They are peripheral nerves from the brain stem and supply muscles of face, nose etc.
Cranial nerves for physio
FACIAL NERVE 7= Supplies muscles of the face- damage to facial nerve can cause Bells Palsy, so dropping of face on one side. Inflammation of facial nerves (mimics stroke).
VAGUS NERVE 10= controls heart, lungs and gastrointestinal system , so damage impacts heart and lungs
Can peripheral nerves mend.
Peripheral nerve can mend but CNS nerves can’t
How many peripheral nerves and cranial nerves are there?
31 spinal peripheral nerves
12 cranial nerves
Autonomic nervous system
Involuntary
SYMPATHETIC - From thoracic + lumbar
Fight or flight so increase HR, breathing rate , shunts blood to muscles
PARASYMPATHETIC- cranial and sacral nerves
Rest an digest so slows HR, lower blood pressure , slow resp rate
What systems does ANS control?
BLOOD PRESSURE HEART AND BREATHING RATE BODY TEMPERATURE DUGESTION METABOLISM WATER AND EKECTROLYTE BALANCE PRODUCING BODY FLUIDS URINATION SEXUAL RESPONSE
Spinal cord damage and regions
Dorsal columns - usually sensory
Lateral and anterior = usually motor info
Connective layers of nerves
EPINEURIUM- Dense CT surrounds whole neurones. Contains vascular networks.
PERINEURIUM- Sheath of CT around fascicles of nerve fibres. Fascicles contain neurones (myelinated or unmyelinated)
ENDONEURIUM- Delicate CT around myelin sheath of axons of nerves.
Structure of a nerve
MIXED NERVE= All spinal nerves are mixed. Contain both afferent (sensory) and efferent (motor) fibres to and from spinal cord.
BASIC NEURONE TYPES
BIPOLAR
eg, interneurone that passes info from one nerve to another
UNIPOLAR
Sensory nerve
MULTIPOLAR
Motor neurone
Features of basic neurone
DENDRITES - Bring info into cell body from receptors
CELL BODY- Contains mitochondria, nucleus and nucleolus. Golgi produces neurotransmitters.
AXON- takes info from cell, body
SYNAPTIC KNOBS= Release neurotransmitters into synaptic cleft from synaptic vesicles
TELODENDRIA- End branches of neurone ends in synaptic knob
Axon covered in myelin sheath from schwann cells in PNS and fatty produce from oligodendrocytes in CNS
What are neuralgia?
Neuroglia connect nerves together for insulation + protection - cells between nerve cells.
Neuroglia cells in PNS
Satellite cells and Schwann cells
Neuroglia cells in CNS
Astrocytes, microglia and oligodendrocytes
Astrocytes
In CNS, astrocytes connect neurones to blood vessels + filters blood so bad substances don’t enter brain.
Holds nerve cells together too.
Microglia
In CNS, spider - like phagocytes to remove debris
Oligodendrocytes
In CNS, they produce myelination, and cover + protect axons in CNS nerves
Schwann cells
In PNS, Schwann cells produce myelin to wrap round axon and protect axon
Satellite cells
Satellite cell function - maybe repair and provide nutrients to neurone?
Why can peripheral nerves regenerate and CNS nerves can’t?
Oligodendrocytes don’t have a neurolemma but Schwann cells do have a neurolemma.
Neurolemma is a structure for the PNS nerves to regenerate if harmed
How does someone recover from a stroke?
CNS nerves don’t repair but we have neuroplasticity in brain- bypassing of information so new pathways created in brain
Nerve conduction in three simple steps
Dendrites transmit electrical impulse into cell body
Cell body produces action potential to pass down axon
End of axon= neurotransmitters released from synaptic vesicles in knobs
Impulse transmitted to adjacent cell
Define nerve impulse
Nerve impulse is electrical current passed down dendrites or axons due to ion channels opening in the plasma membrane.
Action potential sequence
Neurone at rest = inside more negative, as more Na+ outside the neurone
Membrane is polarised at -70mv resting state
Resting potential maintained by sodium-potassium pump. Potassium ions in and sodium ions out.
Stimulus disturbs dendrite plasma membrane + sodium ion channels open
Sodium ions diffuse into neurone
Membrane depolarised at -55mv and increases more so net positive charge in neurone than outside. Wave of depolarisation along the membrane.
Potential difference gets to +30mv, sodium ion channels close and K+ channels open. Repolarisation occurs.
Rapid diffusion if K+ ions out of cell to decrease potential in neurone membrane.
Potassium ion channels slow to close so many K+ diffuse out of cell.
Potential difference is more than resting potential (below -70mv) called hyperpolarisation
Sodium- potassium pump returns membrane back to resting potential and maintains it until nerve stimulated again.
What is refractory period?
Time delay between one ap and the next ap.
Ion channels recover in this time and nerve cannot be stimulated in this time.
It means that:
Action potentials don’t overlap
Limit to frequency of impulses passed
Action potentials unidirectional
All or nothing law
If threshold reached at -55mv, action potentials will always fire with same voltage. Sodium ion channels open and at -55mv the rest of sodium ion channels open
If threshold not reached, then action potential will not fire!
What is spatial summation?
Many impulses arrive simultaneously at cell body and stimulates action potential (many short signals at many dendrites).
If they arrived separately they are weak and threshold not exceeded so no action potential.
What is temporal summation?
Impulses arrive in quick succession one after the next. So series of signals at one synapse can lead to action potential.
What ions are needed for nerve impulses ?
Sodium
Potassium
Calcium
Describe myelinated peripheral N
Myelin sheath around axon - electrical insulator
Sheath is made of Schwann cells with small gaps called nodes of ranvier.
Saltatory conduction- cytoplasm conduct electrical charge to depolarise next node + impulse jumps from node to node
Rapid !
Describe unmyelinatwd neurone
Impulse travels as wave of depolarisation the whole length of axon
Slower than myelinated
Define synapse
The junction between a neurone and another neurone or effector cell
Can neurotransmitters be recycled ?
YES
they’re re up taken into presynaptic neurone to be used again
Enzymes can break neurotransmitters down and components re enter the presynaptic neurone
Define neurotransmitters
Proteins that pass a chemical signal from one neurones axon to next cell
Synapse
Action potential at end of neurone
Calcium ion gated channels open on ore membrane
Calcium ions enter synaptic knob
Influx of calcium stimulates synaptic vesicles to fuse to pre membrane
They release neurotransmitters into cleft
Neurotransmitters bind to receptors on post synaptic membrane
Action potential stimulated in next cell as excitatory or inhibitory
Examples of neurotransmitters
ACETYLCHOLINE - excitatory at neuromuscular junctions - muscle contraction occurs
SEROTONIN- more serotonin in brain, less chance of depression
DOPAMINE- Lack of dopamine causes Parkinson’s . Too much dopamine is schizophrenia
NOREPINEPHRINE- neurotransmitter and also a stress hormone
GABA- neurotransmitter to reduce activity of brain neurones and CNS. Increases relaxation, reduces stress, boosts sleep, produces calmer mood and alleviates pain.
Excitatory neurotransmitters
They will excite next membrane producing AP, by depolarisation
Inhibitory will hyperpolarise membrane to prevent action potential in post synaptic membrane
A stroke patient may have too many excitatory transmitters so high tone and spasticity.
OR too many inhibitory neurotransmitters so weakness and less excitation of muscles
CNS DAMAGE
CNS neurones can’t repair
Clean up slow, oligodendrocytes inhibit regeneration + environment poor
Neuroplasticity - forms new pathways in brain
Structural neuroplasticity
Strength between neurones in the brain are changed
Functional neuroplasticity
Permanent changes in synapses due to learning and development
PNS REGENERATION
Some regeneration
Clean up of damage quicker by macrophages
Schwann cells assist regeneration
Myelinated neurones have neurolemma so can repair, regenerate the axon etc, only if cell body and Schwann cells intact.
How does PNS regenerate?
24-48 hrs chromatolysis so cell body swells
Wallerian degeneration - distal part of axon degenerates and macrophages engulf degraded axon and Schwann cells.
Neurolemma cells divide + form regeneration tube.
Axon sends buds into network of Schwann cells.
Axon grows along cord of Schwann cells
Axon regenerate by wallerian regeneration
PERIPHERAL NERVE INJURIES
Tea with (NaN)
TRANSIENT ISCHAEMIA- lack of oxygen to area supplied by that nerve eg, laying on arm and getting spins and needles in the hand
NEUROPRAXIA - Compression of nerve so blocks nerve conduction. Loss of sensory and motor function for 6-8 weeks. Numbness tingling and vibration.
Usually due to trauma to body but axon not damaged and ANS not damaged.
AXONOTMESIS- commonly in car crash.
Injury to peripheral nerve at an extremity of the body. Axon and myelin sheath damaged but Epi,peri and endo neurium intact. No nerve conduction distal to site of injury for 3-4 days. Some wallerian regeneration but may require surgery.
NEUROTMESIS- Total severance to entire nerve eg, industrial accident. Axon and sheath separated and surgery is needed. Potentially some regeneration but not all.
Complete loss of sensory and motor function
