principles of nervous system 2 Flashcards
How are spinal nerves organised?
segmentally
What is meant by spinal nerves being segmentally organised?
- one pair of spinal nerves at each vertebrae
What are the names of the different areas of spinal nerves? How many are there for each?
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
Describe how the nerves are organised at the cervical area?
- only 7 cervical vertebrae
- C1-7 exit above vertebrae
- C8+ exit below
How do spinal nerves connect to the spinal cord?
via nerve roots
Where do nerve roots sit?
within the vertebral canal
What are the two roots that connect to the spinal cord?
- ventral root
- dorsal root
What type of axons come in through the ventral root?
- efferent
- motor and sympathetic
What type of axons come in through the dorsal root?
- afferent
- somatosensory
What does it mean that spinal nerves are mixed nerves?
they contain motor, somatosensory and sympathetic axons
Where do spinal nerves exit through?
intervertebral foramen
What can be said about the length of a spinal nerve?
they are very short
What can spinal nerves be divided into?
- dorsal/posterior primary ramus
- ventral/anterior primary ramus
What do dorsal primary rami supply?
- skin over paravertebral gutter
- erector spinae muscles
- facet joints of vertebral column
What do ventral primary rami supply?
the rest of the body except parts of head/neck
How do the sizes of nerves between the ventral and dorsal primary rami compare?
ventral primary rami nerves are much bigger
What do ventral primary rami form?
- intercostal nerves
- 4 nerve plexuses
What is a nerve plexus?
where ventral primary rami merge to form nerves that contain axons from multiple spinal nerves
What are the nerve plexuses important for?
the innervation to limbs (large muscles)
What are dermatomes?
individual strip of skin innervated by a single spinal nerve (primary ramus)
What is a myotome?
individual muscle group innervated by a single spinal nerve (primary ramus)
What do dermatomes and myotomes develop from?
- somites
What are somites?
paired blocks of paraxial mesoderm that form in horizontal bands
What is the relationship between somites and spinal nerves?
one pair of spinal nerves grows into one pair of somites
What are the T1-T11 dermatomes supplied by?
the intercostal nerves (which come from ventral primary rami)
What is the significance of the T10 dermatome?
it is where the umbilicus is
What does a changed sensation from a dermatome indicate?
injury to the spinal cord, nerve root or spinal nerve
How can dermatomes help with viscera pain?
viscera pain can be referred to skin dermatomes as cutaneous pain
What are the intercostal muscles supplied by?
the intercostal nerves (T-T11)
What is the autonomic nervous system?
the involuntary part of the peripheral nervous system
What does the autonomic nervous system do?
- regulates operation of the internal organs
- maintains internal environment
- innervates smooth muscle, cardiac muscle, glands
What are the two main divisions of the autonomic nervous system?
- sympathetic
- parasympathetic
What does the sympathetic system do?
- fight or flight response
- maximises use of metabolic resources
What does the parasympathetic system do?
- opposiite to sympathetic
- switched on during resting
- conserves metabolic resources
What is the origin of the parasympathetic system?
- brainstem
- sacral spinal cord
What is the origin of the sympathetic system?
thoracic spinal cord
What is autonomic ganglia?
where preganglionic neurons synapse with postganglionic neurons
Are preganglionic and postganglionic neurons myelinated or not?
- preganglionic are myelinated
- postganglionic are unmyelinated
Describe the anatomy of the autonomic nervous sytem?
- usually two neurons in a circuit
1. preganglionic neuron
2. autonomic ganglia
3. postganglionic
4. effector organ
What is the exception to the usual 2 neurons in a circuit structure of the autonomic nervous system?
- sympathetic supply to the adrenal gland
- its preganglionic axons only
What are some things the sympathetic division controls?
- cardiac muscle
- bronchi of lungs
- sweat glands
- hair follicles
- blood vessels
- abdomino-pelvic viscera
- eye
Where are the cell bodies of the preganglionic neurons found in sympathetic division?
the thoracic and lumbar spinal cord (T1-L2)
Where do the preganglionic axons exit (sympathetic)?
via ventral roots to enter spinal nerves
What is the sympathetic trunk?
- interconnected paravertebral ganglia
- extends length of vertebral column
Where do the preganglionic axons go after entering the spinal nerves (sympathetic)?
- enter sympathetic trunk
- synpase with postganglionic neurons
What is the ratio of preganglionic neurons to postganglionic neurons?
1:20
Where can the postganglionic axons go from the sympathetic trunk?
- primary rami (to musculoskeletal system)
- branches (to heart, lungs or head)
What do some preganglionic axons do rather than end at he sympathetic trunk?
- pass through sympathetic trunk
- enter splanchnic nerves to prevertebral ganglia in abdomen
- here postganglionic axons innervate abdominal/pelvic organs
In the cranial parasympathetic, where are the cell bodies of the preganglionic neurons found?
brainstem
Where do cranial preganglionic axons go after leaving the brainstem? (to innervate head)
- pass through cranial nerves to ganglia in head
- postganglionic neurons innervate structures in head
Where do cranial preganglionic axons go after leaving the brainstem? (to innervate thorax/abdomen)
- preganglionic axons pass through vagus nerve to thorax and abdomen
- postganglionic axons innervate viscera
In the sacral parasympathetic, where are the cell bodies of the preganglionic neurons found?
- sacral spinal cord
Where do sacral preganglionic axons go after leaving the sacral spinal cord?
- pass through pelvic splanchnic nerves
- post ganglionic axons innervate pelvic viscera
What are the pelvic organs?
- bladder
- rectum
- sexual function
