BL 20 Flashcards
Basic layout of the nervous system
Somatic nervous system
The somatic nervous system (SNS or voluntary nervous system) is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The somatic nervous system consists of afferent nerves or sensory nerves, and efferent nerves or motor nerves
What is the autonomic nervous system?
The autonomic nervous system is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal. It contains three anatomically distinct divisions: sympathetic, parasympathetic and enteric.
What is the sympathethic nervous system?
FIGHT OR FLIGHT SYSTEM
The sympathetic nervous system directs the body’s rapid involuntary response to dangerous or stressful situations. A flash flood of hormones boosts the body’s alertness and heart rate, sending extra blood to the muscles.
What is the parasympathetic autonomic nervous system?
REST AND DIGEST SYSTEM
The parasympathetic system conserves energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract.
What is the enteric nervous system?
Intrinsic nervous system in the gut
Major role is to transmit food from mouth to anus
Sturcture of individual segments in the spinal cord
- Dorsal root
- Ventral root
- Central canal
- White matter
- Grey matter
- Spinal nerve (SN on diagram)
What is the dorsal root?
Connecting to the back of the spinal cord, purely sensory
What is the vental root?
Connecting to the front of the spinal cord, purely motor
Spinal nerve - what is this?
Nerve after motor and sensory neurones have joined
(spinal nerves are composed of both sensory and motor fibers (mixed nerves))
What is a gangolion?
Collection of cell bodies in the peripheral nervous system
What nerves cell bodies are in the spinal ganglion?
Sensory neurone
How many spinal cord segments are there? How many spinal nerves are there?
31 segments in a spine
31 spinal nerves
How is knowing the segments of the spinal cord helpful?
For each one of the spinal nerves, there is a discrete region of the skin (dermatome).
For each one of the spinal nerves, there is a discrete region of muscle (myosome)
Where does the spinal cord go from and to?
from the foremen magnium to L1 vertebrae
Cauda equina?
Cauda equina (from Latin horse’s tail) is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which arise from the lumbar enlargement and the conus medullaris of the spinal cord.
Describe a reflex arc (include the two or three types of nerves involved, the roots, where the cell bodies are located for all nerves, where the other structure the move into is called…)
- Dorsal horn connects to the peripheral nervous system via the dorsal root (dorsal root is sensory). Posterior
- Ventral horn connects to the peripheral nervous system via the ventral root (ventral root is motor)
- Ventral root and dorsal root come together to form the spinal nerve (spinal nerve is a mixed sensory and motor neurone…) Anterior
- Spinal ganglion: This is where the cell bodies of the sensory neurone are
- Motor neurone cell bodies are located in the ventral horn
How does the autonomic nervous system link to the CNS and PNS?
True for sympathetic and parasympathetic system:
- Preganglionic neurone’s cell body is located in the CNS
- Postganglionic neurone’s cell body is located in the PNS
Describe the neurones in the sympathetic system and the target
- Short preganglionic neurone, long post ganglionic neurone
Target - Smooth muscles in blood vessels etc
Describe the neurones in the parasympathetic nervous system? and there target
- Long preganglionic neurone, short post ganglionic neurone
Target: glands
Sympathetic system (where are the cell bodies for these? which part of the spinal cord?)
- Preganglionic neurone cell body is in the lateral horn
- Postganglionic neurone cell body is in the sympathetic chain/trunk (this is close to the CNS)
- Lateral horn in T1-L2 (middle of spinal cord)
Parasympathetic system (where are the cell bodies for these? which part of the spinal cord?)
- Preganglionic cell body is in the brain stem or in the lateral horn of the spinal cord
- Postganglionic cell body tends to be in the wall of the tissue targetted (very long preganglionic neurone) e.g. in the bladder the postganglionic is in the wall of the bladder
Where are the autonomic preganglionic neurone cell bodies found in the CNS? Sympathetic and parasympathic
Sympathetic - Lateral horn in T1-L2 cord segments
Parasympathetic - S2-S4 cord segments and brainstem
How the sympathethic autonomic system is all connected - drew this out in the lecture
- Pre-ganglionic neurone’s cell body is in the lateral horn
- pre-ganglionic neurone goes along the ventral root
- pre-ganglionic neurone goes through white ramus communications (W in pic below)
- cell body of post-ganglion neurone in the sympathetic ganglion
- post-ganglionic neurone goes through grey ramus communicans (G in pic below) and into the spinal nerve
- post-ganglionic neurone then goes to target tissue
Sympathetic nervous system - Distribution to the skin, use of the sympathetic trunk
Sympathetic preganglionics arising in the T1-L2 cord segments supply the skin via one of the following three routes:
•Synapse at the level of entry (to supply dermatomes at the T1-L2 levels). Postganglionics get to their targets through the T1-L2 spinal nerves. As the pre-ganglionic neurones are at the level of entry, they do not have to ascend or descend the sympathetic trunk.
•Ascend the chain then synapse (typically to supply the head and neck). Postganglionics get to their targets along the walls of blood vessels.
The pre-ganglionic neurones don’t start until T1, they therefore have to ascend the sympathetic trunk and synapse at a sympathethic ganglionic further up the body. The post-ganglionic neurone then tasks the message to the correct level.
•Descend the chain then synapse (typically to supply the lower limbs). Postganglionics get to their targets through the spinal nerves at levels L3 and below.
The pre-ganglionic neurones finish at L2, they therefore have to descend at the sympathetic trunk and synapse at a sympathethic ganglionic further down the body. The post-ganglionic neurone then tasks the message to the correct level.
Sympathetic nervous system - Distribution to the abdominal viscera (internal organs)
DON’T SYNAPSE IN THE SYMPATHETIC CHAIN FOR DISTRIBUTION TO ABDOMINAL VISERA
- Sympathetic preganglionics go straight through the sympathetic chain (and don’t synapse), they then form specialist nerves called splanchnic nerves.
- Splanchnic nerves synapse at the pre-aortic ganglion
- Postganglionics get to their targets (i.e. abdominal viscera) along blood vessels
• Sensory fibres also travel along sympathetics destined for the abdomen and relay pain from viscera back to the CNS (two way traffic), but mainly describe it as a motor system
Parasympathetic nervous system (where do the preganglionic neurones synapse? give examples in head and neck)
Parasympathetic preganglionic neurones typically synapse in ganglia that sit close to their target organs (often in the wall of the target)
The major source of parasympathetic preganglionic input to the thoracic and abdominal viscera is the vagus nerve
The head and neck has four specialised parasympathetic ganglia:
• The ciliary ganglion receives parasympathetic preganglionics from the oculomotor nerve and distributes parasympathetic postganglionics to the eye
• The pterygopalatine ganglion receives parasympathetic preganglionics from the facial nerve and distributes parasympathetic postganglionics to the lacrimal gland
• The submandibular ganglion receives parasympathetic preganglionics from the facial nerve and distributes parasympathetic postganglionics to the submandibular and sublingual salivary glands
• The otic ganglion receives parasympathetic preganglionics from the glossopharyngeal nerve and distributes parasympathetic postganglionics to the parotid gland
