WEEK 8 NERVOUS SYSTEM Flashcards
What does the PNS consist of ?
Cranial nerves (12 pairs)
Spinal nerves (31 pairs) : 8 cervical 12 T, 5L, 5S, 1coxygeal
Ganglia
Plexuses
How are spinal nerves named?
Based on the segment or region of body they supply
What are ganglia?
Discrete clusters of neurons distributed outside the CNS and occur across body
What is special about the cervical vertebrae and nerves?
There are 8 cervical nerves but only 7 cervical VERTEBRAE
What is the input part of nervous system and what does it do?
Sensory division, transmits stimuli from receptors (secialised ends on neurons)
What are the two components that sensory can be divided into?
Somatic sensory and visceral sensory
What does the somatic sensory component do?
Transmits sensory inputs from strucutres in body wall (anything that isn’t an organ) - touch and temperature, pain, pressure, vibration
What does the visceral sensory component do?
Transmits impulses from blood vessels, viscera to the CNS (temperature and stretch) and sensory input from visceral organs like heart blood vessels GI tract.
- has much narrower range of receptors so can only receive certain types of stimuli
What is the output part of the CNS?
Motor division
What does the Somatic Motor system do?
Transmits nerve impulses to skeletal muscles
What is the ANS associated with and what does it innervate?
Visceral organs and vessels
- Innervates smooth & cardiac muscle tissue, and glands
What is nervous tissue?
Its own type of tissue that comprises of neurons and glial cells
What are glial cells?
Non excitable cells (support and protect neuron)
What does the soma do?
(body) receives, integrates, and initiates impulseds
What do dendrites do?
Contain the synapses (communication b/w individual neurons) - receptive region of neuron
What do axons do?
Transmission pathway for impulses generated by the soma, towards other neurons or target organ
What are multipolar axons?
Have one single axonal process e.g. motor neurons
What are unipolar neurons?
Have two exonal processes extening from soma .e.g. sensory neurons
What are examples of bipolar neurons?
In the special sensory crainial nerves such as ganglion of vestribulocochlear nerve
Are dendrites, synaptic nobs, and soma myelinated or unmyelinatetd?
unmyelinated to receive and transmit signals
Why are myelinated parts of neurons white?
Because of fats within neurolimicytes
What colour areunmyelinated parts?
Gray
What is the ventral horn of gray matter for?
Motor division
What is the dorsal horn of gray matter for?
Sensory division
What does ventral white matter represent?
Motor axons and descending pathways
What does dorsal white matter represent?
Sensory axons and ascending pathways
What types of nerves are spinal nerves?
Mixed nerves composed of both motor and sensory components
What are the roots of the spinal cord?
Myelinated axons (dorsal and ventral) that are EITHER motor or sensory- no mixing of motor and sensory unitl further down
What does the dorsal root ganglion function as?
To house the first order neurons (unipolar neruons), have long axonal processes in peripheri detecting sensations and the shorter axonal process extending from dorsal root ganglion to dorsal horn of spinal cord
Where is the mixed spinal nerve found?
Just lateral to the spinal cord
Which structure is the first to house mixed nerves?
The dorsal and venrtral rami (ramus for singular)
What is endonerium?
Delicate layer of loose connective tissue -each myelinated nerve is wrapped around this
What is perinerium?
Bundles of nerve fibre wrapped in this (cellular and fibrous layer) to form fascicles
What is epinerium?
Wraps around the fascilcles (dense irregulave connective tissue covering the ENTIRE NERVE)
Do nerves contain blood vessels?
YES they require vascularisation
What is the brain continuous with?
The brainstem
What does the ectoderm becom after development?
epidermis of skin and CNS
What does the endoderm become?
Lining and inside of GI tract
What does the mesoderm form?
Most of the tissues–> in development, turns into series of blocks called somites (31 pairs) which becomes the mixed spinal nerves - dermatomes- strips of segments
Why does segmentation become difficult with limbs?
Because limbs are outgrowths from the midline axis
What does the sclerotome (division of somite) form?
Bone (tough part)
What does the myotome (division of somite) form?
Forms skeletal muscle
What does the dermatome (division of somite) form?
The dermis (deep to epidermis)
What happens when the nervous system is formed?
The axon is grown out from CNS to reach target which could be a sclerotome
Why do nerves exit between adjacent vertebrae
Growing axons coming out of CNS are going to split the sclerotome (tissue that forms bone) to reach other components- also reason why we experience pinched nerves in back-space where nerves exit is very narrow
What is the dorsal root ganglion derived from?
Neural crest cells -that is why it is isolated
Where does the dorsal root ganglion rest?
In epidural space
Why does injecting anaesthetic into the epidural space cause for pain relief?
Because the dorsal root ganglion rests here, so the injection is targeting the ganglion. This BLOCKS the transmission of signal to SEGMENT that that section (vertebral level) supplies (segmentaion)
Where does the epidural space lie?
Between the periosteum and dura mater
Where does the subarachnoid space lie?
B/w arachnoid and pia mater (contains CSF and nerve roots)
What is the CSF critical for?
Maintaining the CNS, waste transmission out of the CNS, metabolites
What is used to anchor the spinal cord?
(denticulate ligamnets) Extensions of pia mater off the surface of the spinal cord and at regular intervals, extend it out to the lateral aspects and attach it to dura mater. Minimises movement of spinal cord in vertebral canal
What is the conus medullaris?
A swelling at the most inferior end (triangular cone like expansion)
What are filum terminale?
Extension of pia mater that anchors spinal cord in position and attaches to the coccyx (pia mater collapses in on itself because at this point there is no spinal cord)
What is the cauda equina?
Collection of nerve roots that will go into the lower limbs and pelvis (horses tail) - individual sets of axons that haven’t reached targets yet but in enclosed space bathed by CSF
Why is inserting a needle to draw CSF much safer at the cauda equina level (L2) ?
Because the spinal cord has already terminated at L1 so injecting a needle at L2 without spinal cord is less likely to cause damage to CNS. NOTE** doesn’t apply to all adults and doesn’t apply to children
Why cant you inject needle into L2 in children?
Positioning of strucutures will differ
How is the white matter organsised in the spinal cord?
Decreses in size caudally and arranged in laminae (C,T,L)
What pathways is the dorsal (posterior) tract (spinothalmic)?
Ascending sensory pathways
What pathways is the ventral (anterior) tract (cprticospinal)?
Mainly descending motor pathways
What is the lateral tract and which spinal levels is it located?
Mixture of ascending and descending pathways
Which levels is the lateral horn located and what does it give rise to?
b/w T1-L2 (sympathetic outflow) and S2-S4 (parasympathetic outflow (17 levels)
Where is the signal to perform voluntary movement originating from?
Brain-primary cortex
What is the ANS defined as?
A two neuron system -always two visceral motor neurons b/w CNS and effector
What is the preganglionic neuron in the ANS?
Soma in gray matter of CNS; axon to ganglionin PNS (between CNS and ganglion)
What is the postganglioninc neuron in the ANS?
Runs from the ganglion to the organ (soma in ganglion in PNS axon projects to effector)
Where does the synapse between two motor neurons occur in the (ANS)?
In an autonomic ganglion`
Which two regions does the parasympathetic preganglionic fibres orginiate?
In the brain (CN II,CN VII, CN IX, CN X) and in the region S2-S4 (sacral parasympathetic)
Where do the sympathetic preganglionic fibres originate?
In the lateral horn of spinal cord in T1-L2
What is the alrget most widely distributed parasympathetic nerve?
Vagus nerve; heart, liverm stomach, GI tract, etc.
What are the differences between the sympathetic and parasympawthetic pathways?
Parasympathetic pathway has vagus nerve that doesn’t synapse until it reaches target organ, so VERY LONG preganglionic fibre and VERY SHORT post ganglionic fibre (as ganglion is basically embedded in organ)
Sympathetic has very short preganglionic fibres and long postganglionic fibres
What is the primary somato sensory cortex responsible for?
Integrating sensory info coming in from body
Where do sympathetics originate?
T1-L2 - lateral horn of spinal cord
What does the telencephalon form?
Cerebrum
What does the diencephalon form?
Diencephalon which includes thalamus
What does the mesencephalon form?
The midbrain (tectum and tegmentum)
What does the Metencephalon form?
Pons/ cerebellum
What does the mylencephalon form?
Medulla oblongata
What are clusters of cell bodies called IN THE CNS?
Nuclei
What doe the cerebellum communicate with the brainstem via?
The cerebellar peduncles
Why does the epithalamus (pineal gland) have degraded retinal cells?
Because it was the light patch on the surface of brain that detects light to let animal know it was daytime
Why is the epithalamus not on surface of brain anymore and can’t see light?
Because of the massive overgrowth of the telencephalon (so it is sunken in our brain) - cerebreum is part of telencephalon
Is the optic nerve a true nerve
No it is a direct extension from the brain
What does the occulomotor nerve innervate?
4 extraoccular eye muscles and the upper eyelid, and parasympathetic innervation to pupil (constriciton) and lens (spherical for near vision)
What type of nerve is the trigeminal?
Mixed sensory and motor
What is V1 and what type of nerve?
Opthalmic- snesory from cornea, nose, forehear, scalp
What is V2 and what type of nerve?
Maxillary- sensory for inside of mouth, gums, cheek, nasal mucosa
What is V3 and what type of nerve?
Mandibular; sensory from anterior tongue, skin of chin, mandible, auricle of ear and MOTOR FOR MUSCLES OF MASTICATION
What does the facial nerve innervate?
It is motor and sensory and innervates anterior 2/3 of tongue taste and parasympathetic to lacrimal and submandibular/sublingual salivary glands (increases output)
What does the vagus nerve innervate?
Mixed sensory and motor:
Sensory innervation from heart, lungs, pharynx, larynx, GI tract to left colic flexure
Motor: Muscles of pharynx and larynx
Parasympathetic: Visceral smooth muscle, cardiac muscle, glands of heart, lungs, pharynx, larynx, trachea, and abdominal organs.
What does the spinal nerve innervate?
Motor nerve: Crainial root: Travels with vagus nerve to pharynx, Spinal root: innervates sternocleidomastoid and trapezius muscles
What does the hypoghlossal Cn XII innervate?
Motor innervation to extrinsic and intrinsic muscles of tongue - speech and sound shaping
What is the function of the cerebellum?
Remembers pattern movements and locations and fine motor movements; without one you don’t have refined movements; refines motor output that the cerebellum is generating (voluntary signals)
What is the anatomy of the cerebellum?
2nd largest part of the brain, cortex (outer region) of gray matter and is deeply folded- arbour vitae, lots of cortico S.A in small amount of space
What is the function of the Pons (part of metencephalon)?
‘redistribution centre’, receives axons from the rest of the brain in descending tracts from cerebrum and ascending tracts across the medulla oblongata and spinal cord ; pons connects cerebrum to cerebellum
What is the anatomy of the pons?
White matter (myelinated axons) and superior to medulla oblongata
What is the function of the mesencephalon (midbrain)?
visual and auditory reflexive actions (tectum), tegmentum does involuntary motor movements like eye movement, sleep/wake cycle, and contains the substansia nigra- addictive centre (reward seeking behaviour), and contains red nucleus which is involved in postral muscles (bipedal movement, standing erect)
What is the anatomy of the mesencephalon(midbrain)?
Last part of defined brainstem, b/w pons inferiorly and thalamus superiorly , tectum contains 4 swellings called colliculi- auditory is inferior colliculus
What does the diencephalon contain?
Contains thalamus which has 3 separate zones
What are the 3 zones of the diencephalon?
Thalamus, Epithalamus (posterior aspect of thalamus),and hypothalamus (inferior surface)
What does the thalamus in the diencephalon do and what is the anatomy?
Receives sensory input such as tingling fingers to then be redirected out to location in cerebrum - anatomy is large cluster of somar gray matter)
What does the epithalamus in diencephalon do?
Known as the pineal gland and releases melatonin (sleep wake cycle)
What does the hypothalamus in diencehalon do?
Direct bridge between endocrine and nervous system- controls secretions through pituitary gland- homeostasis
What is the anatomy of the cerebrum as part of telencehpalon?
Separated into two halves by longitudinal fissure and this is further divided into lobes. Lots of cortical folding (folding of cortex) to increase S.A for gray matter- neurons (not just about the size of the cerebrum but the amount of folding-encephalisation)
What are the 5 lobes of the cerebrum (of the telencephalon)?
Frontal, parietal, temporal, occipital, insula
What does the frontal lobe do and location?
Contains primary motor cortex and associated with higher order learning and function (disproportionately increases in humans)- anterior to central sulcus
What does the parietal lobe do and location?
Contains primary somatosensory cortex - processes complex semantic parts of LANGUAGE and posterior to central sulcus
What does the tmeporal lobe do and locaton?
Hearing and patterns of speech. Integration of auditroy and audo-visual. Inferior to lateral sulcus
What does the occipital lobe do and location?
Visual processing. Posterior pole of each hemisphere.
What does the insula lobe do?
Processes taste, vestibular (balance), and visceral sensation.Not visible from external surface-deep to temporal, frontal, and parietal lobes and discrete section of insular cortex (gray matter)
