3 - The Nervous System Flashcards
What is the CNS and PNS?
CNS = spinal cord and brain PNS = 12 cranial nerves and 31 spinal nerves
What is the somatic nervous system?
Controls skeletal muscle under voluntary control including both incoming sensory (afferent) and outgoing motor (efferent) fibres from the brain and spinal cord
What is the autonomic sensory system?
A division of the PNS that controls internal organs and the flight/flight response. Divided into
sympathetic: stimulates nervous activity (has pre/post ganglionic neurons)
parasympathetic: slows down the nervous system
What is ganglia?
Ganglia are a group of cell bodies, from a number of segmental levels, or nerve cluster that occurs in the PNS. They act as intermediates between the PNS and CNS i.e. dorsal root ganglia. Should think about what territory is this ganglia supplying. Big nerve bundles.
What is a plexus?
Branching network of nerves/vessels. Cervical, brachial, lumbosacral. Arise from the anterior rami of spinal nerves
What is a dermatome and what is a myotome?
Dermatome = area of skin supplied by the cutaneous branches of a single nerve. This can be mapped in the body and is used to measure spinal cord damage Myotome = the muscles innervated by a single spinal
What are the spinal nerves?
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
What are the layers of the meninges and spaces?
Epidural space: Dura Mater: Subdural space: Arachnoid Mater: Subarachnoid space: Pia Mater:
Epidural Space?
Contains fat which is the last to go. Small blood vessels with more veins than arteries. Put anaesthetics in here as is close to nerves but don’t have to penetrate tough dura mater. Between dura mater and vertebral wall
Dura Mater
Robust, tough fibrous tissue that the scalpel struggles to get through. Tough mother.
Subdural Space
VIRTUAL SPACE as dura mater and arachnoid are very close. Few arteries and veins. If you get brain shrinkage can get the space opening up and can tear the veins causing subdural haemorrhage. Short confusion and black-out - small bleeds
What is a single segmental level?
Level at which a single spinal nerve leaves. Think cross section
Why 8 cervical nerves but 7 vertebra?
1st comes out between skull and first vertebra
When does the spinal cord finish?
At L1. At this point becomes cone shaped = Conus Medularis ends the spinal cord. From here on it is the Cauda Equina
What direction does the spine protect the spinal cord?
Forwards and backwards but not elongation of spinal column - stops us being rigid. Structures in the spinal cord anchor it in place. If it wasn’t and you bent over the spinal cord would stretch and you would experience pain like a slipped disc everywhere
Arachnoid Mater?
Web-like, shimmery nodes connect it here and there
Subarachnoid space
IMPORTANT - lots of CSF. Largest reservoir
Pia Mater
So closely adhered to spinal cord and nerves that you can’t distinguish it visually. Soft.
What are the spinal nerves (motor and sensory) surrounded by?
A blend of the meninges. Epineurium.
What are the sensory neurons?
Pseudounipolar neurons. Discriminative and non-discriminative.
What is a spinal nerve?
A combination of the dorsal root and ventral root that will supply/take information to a particular level
What are the 3 places the spinal nerves come from or go to?
- Posterior Ramus: innervates back musculature. Small branch as small area.
- Anterior Ramus: supplies muscles and organs of the front
> both voluntary - Ramus Communicans: connects the spinal cord and the autonomic nervous system. It is a nerve that connects other nerves
> involuntary
What happens at the conus medullaris?
Spinal cord ends at conus medullaris at L1. A fibre continues and anchors into the coccyx. This is called the Filum Terminale (more white/blue and tighter than the other fibres). The Filum Terminale is a coming together of all the pia mater like the end of a sausage. It anchors and supports the spinal cord so when you bend over you don’t stretch the vertebral levels out of place
Difference between discrim and non?
Discrim = what can you feel in the periperhy thats different at A than B Non = responds to noxious stimuli that you should withdraw from or change behaviour
What happens to the subarachnoid space after the conus medulairs?
The subarachnoid space and so CSF continues down with the filum terminale until S2 which is the lower limit of the subarachnoid space. Here the arachnoid mater also comes together around the pia mater to help form the filum terminale. This means all the CSF is above S2.
What is the clinical important of the cauda equina and CSF filled subarachnoid space?
- if need some CSF (protein or bacteria or virus - meningitis - would accumulate around meninges)
- At the level of conus medullaris the chance of hitting the spinal cord is high as it is bigger
- at cauda equina you are less likely to hit a nerve or if you do it will likely bounce of the nerves and miss (may get twinge in leg)
Where is the filum internum and externum?
Internum is above the lower limit of the subarachnoid space where there is CSF
Externum is below the lower limit where there is no CSF and the fibre consists of BOTH pia mater and arachnoid
Denitculate Ligaments
- the arachnoid goes back and forth from being attached to the dura mater and the pia mater
- the arachnoid mater is attached to these by the denticulate ligaments (tooth like)
- if you didn’t have the ligaments then the arachnoid mater would close IN if the pressure increased or open more if pressure dropped. The ligaments give structure and ensure there is a CONSTANT volume of CSF around the spinal cord
Ganglia?
Large bunch of nerves that come together from a group of spinal nerves - synonymous with plexus.
