Neurophysiology 2 Flashcards
The spinal chord
*Protected by the Vertebral column
*From base of skull to 1st /2nd lumbar vertebrae
*Nerve roots extend in the lower vertebral region as a bundle of nerve fibres (cauda equina or horse’s tail)
*Regions classified according to the regions of the vertebral column
*Protected by the Vertebral column
*From base of skull to 1st /2nd lumbar vertebrae
*Nerve roots extend in the lower vertebral region as a bundle of nerve fibres (cauda equina or horse’s tail)
*Regions classified according to the regions of the vertebral column
(see diagram in notes)
Peripheral nervous system
Sensory (sensing) and motor (reacting)
Somatic and autonomic
(see innervation pathway diagram in notes)
Cranial nerves
The 12 pairs of cranial nerves transmit information on the senses of sight, smell, balance, taste, and hearing from special sensory receptors.
They also transmit information from general sensory receptors in the body, largely from the head.
These nerves have both motor and sensory fibres and innervate structures in the head and neck with the exception of the Vagus nerve (X) which innervates organs in the thoracic and abdominal cavities
this information is received and processed by the central nervous system. The response then travels via the cranial nerves to the skeletal muscles to control movements in the face and throat, such as swallowing and s
Cranial nerve names and functions
Oculomotor /Abducens / Trochlear / Optic : Eye movement/control/function/ retina
Olfactory - nasal
Vestibular – balance
Hypoglossal/ glossopharngeal – controls tongue and throat
Trigeminal – facial sensation and motorcontrol
Facial – facial gland control – tears and salivary
Accessory – larynx, pharynx, palate, shoulder & neck
Vagus nerve as mentioned previously has many connections
A parkinsons study showed that vagus nerve stimulation reduced symptoms
The vagus nerve is also how covid is transported to the brain
(see labelled brain diagram in notes)
Spinal nerves
Nerve fibres to and from the SC bundled in 31 spinal nerves
Sensory division
Dorsal root, information from muscle, skin into SC and terminates in the dorsal aspect of the cord
Motor division
Ventral root emerges from the ventral aspect of the cord, made up of axons of motor neurons innervating the muscles
The spinal nerves emanate from different areas of the spinal cord and each spinal nerve has a dorsal root and a ventral root.
The dorsal root has sensory (afferent - incoming signals) fibres that carry information from the sensory receptors to the spinal cord with the cell bodies in the dorsal root ganglia.
The ventral root has motor (efferent – outgoing signals) fibres that transmit messages from the CNS to the effectors, with the cell bodies of the efferent fibres found in the spinal cord gray matter.
Somatic nervous system
Somatic nervous system bypasses the brain for a quick response. e.g. reflex arcs:
stimuli from sensory organs (e.g. skin) -> dorsal root ->spinal cord -> ventral root -> muscle
Processing signals via the brain is a longer and slower process required for tuning motor skills such as playing the piano (see diagrams in notes)
Cells of the nervous system - not just neurones!
There are over ~100 billion neurons in the human brain
And ~10 fold more glial cells
Neurons : functional units of the nervous system, generate and conduct the impulses (information), electrically and chemically excitable
Glia provide insulation, nourishment , support
Neuron structure
Dendrites: Derived from the Greek word for ‘tree’
Receives signals from sensory inputs
Covered with synapses (post synaptic)
Pattern of branching one way to classify neurons
cell body (soma)
which has all the components of a normal cell and projections (dendrites and axon)
Neuronal membrane
a lipid bilayer and has specialized proteins embedded – pumps and channels essential for function.
Cytoskeleton
provides structure and allows transport within the cell
Includes microfilaments, microtubules and neurofilaments
Types of glial cells
Astrocytes:
Most abundant glial cells in CNS
hold neurons together, transfer nutrients from blood to neurons, help in forming the blood-brain barrier, repair brain injuries by forming neural scars, help in neuronal function by regulating potassium levels, degrading neurotransmitters, enhance synapse formation and synaptic transmission
Oligodendrocytes:
form insulating myelin sheaths around axons in the CNS
Microglia:
Immune cells, release growth factors like nerve growth factor
They make up the immune system in the brain
Usually inactive, awaiting pathogens
Ependymal cells:
Line fluid filled cavities of the CNS, helps form cerebrospinal fluid, have the potential to form new neurons (neural stem cells)
Schwann cells:
In the PNS, produce thin sheets of myelin that wrap around axons
Excess glial cells can lead to the formation of a glioma and having too few has been linked to memory impairment etc.
Visualising neurones
The first to be observed were perkynje cells the largest of the neurons
10 to the power of 15 synapses present in the human brain
Defects in myelination/ myelin protein disrupt conduction of nerve signals
Poor myelination leads to jittery/shivering movements and eventually paralysis
The mouse model for demyelination (hmcns) was created in the Laboratory of Brian Popko, University of Chicago Medical Center.
Muscle tremor is caused by the neurons not being properly myelinated
Defects in the neuronal cytoskeleton contribute to Alzheimers disease
In Alzheimer’s disease, neurons in the cerebral cortex develop neurofibrillary tangles
An abnormal form of Amyloid precursor protein (APP, a component of the neuronal plasma membrane) known as Ab aggregates into neurotoxic plaques.
This brings about aggregation of the microtubule associated protein – tau into paired helical fragments which forms the neurofibrillary tangles
Normally, tau forms a bridge between microtubules in axons keeping them parallel
In absence of tau the microtubules break down too contributing to the death of the neuron.
Can neurons regenerate
Yes
They are easy to regrow/ grow in lab
However it is difficult to direct their growth and specify the synapse orientations
Contributions of the nervous system to homeostasis
Together with hormones from the endocrine system, nerve impulses provide communication/regulation of most body conditions
Integumentary system:
Sympathetic nerves of the ANS control contraction of smooth muscles attached to hair follicles as well as the secretion of perspiration from sweat glands
Skeletal system
Pain receptors in bone tissue warn of brain trauma & damage
Muscular system
Somatic motor neurons receive instructions from motor areas of the brain and stimulate contraction of skeletal muscles to produce body movements
Basal ganglia and reticular system set level of muscle tone & cerebellum co-ordinates skilled movement (e.g. for sports or playing an instrument)
Endocrine system
Hypothalamus regulates secretion of hormones from pituitary gland
ANS regulates secretion of hormones from adrenal gland & pancreas
Cardiovascular system
Cardiovascular centre in the medulla oblongata provides nerve impulses to ANS that governs heart rate and forcefulness of heartbeat
Hypothalamus also regulates many aspects of heart function
Nerve impulses from ANS regulate blood pressure and blood flow through vessels
Lymphatic system & immunity
Certain neurotransmitters help regulate immune responses
Activity in nervous system may increase or decrease immune responses
Respiratory system
Respiratory areas in brain stem control breathing rate & depth
ANS helps regulate diameter of airways
Digestive system
ANS and enteric nervous system help regulate digestion
Parasympathetic ANS stimulates digestive processes
Also has its own separate regulatory nervous system
Urinary system
ANS help regulate blood flow in kidneys & then urine formation
Brain and spinal cord centres govern emptying of bladder
Reproductive system
Hypothalamus and limbic system controls sexual behaviours
ANS controls erection of penis & clitoris + ejaculation
Hypothalamus regulates release of hormones that control gonads
Nerve impulses elicited by touch stimuli from suckling infant cause release of oxytocin & milk ejection in nursing mothers
Summary
All living organisms can respond to stimuli
Evolution of the nervous system involves:
increasing complexity of reflex arcs, centralization, and cephalization
The vertebrate nervous system can be divided into:
A central nervous system and a peripheral nervous system:
- A central nervous system comprises of the Brain and Spinal cord. Different regions of the brain are associated with different functions
- A peripheral nervous system has an afferent division (sensory and visceral input) and an efferent division (somatic nervous system and autonomic nervous system)which are connected to the CNS by cranial and spinal nerves
Cells of the nervous system include neurons and glial cells
Malfunction of neuronal or glial cells result in neuropathies
