Flashcards in Quiz 2 - The Nervous System Deck (77):
Peripheral nervous system
all of the nervous tissue located outside of the CNS – primarily nerves that function as communication links between the body and CNS
2 types of peripheral nerves
cranial nerves and spinal nerves
collections of neuronal cell bodies that exist outside of the CNS.
In the fully developed spinal cord what two distinct areas are visible in the cross-sectional view?
The gray matter and the white matter
Gray matter of spinal cord
The gray matter resembles the shape of a butterfly and primarily contains neuronal cell bodies. The “wings” of the butterfly are called ventral (anterior) and dorsal (posterior) horns. Some regions of the spinal cord (thoracic, sacral) also have a lateral horn of gray matter that contains neurons associated with the autonomic (visceral) nervous system.
Gray matter consists of neuronal cell bodies
surrounds the gray matter and primarily contains axons that are organized into tracts.
Where is the spinal cord contained?
within the vertebral canal, a channel through the vertebral column.
Spinal cord enlargements
Swellings that reflect the large number of neurons (cell bodies) in that area (more gray matter)
There's the cervical enlargement and the lumbar enlargement
found in the C5-T1 regions of the spinal cord; neurons provide innervation to the upper extremity.
found in the L1-S3 regions of the spinal cord; neurons provide innervation to the lower extremity
The vertebral column consists of ___ vertebrae divided into 5 sections
5 subdivisions of the vertebral column
cervical (w/enlargement), thoracic, lumbar (w/enlargement), sacral, and coccygeal
Why are the sacral and coccygeal regions dubbed the "sacrum" and the "coccyx"?
Because the vertebrae in those regions are fused
How many vertebrae are in each section?
Cervical (7), thoracic (12), lumbar (5), sacral (5), coccygeal (4)
Vertebrae in which regions are separated by intervertebral discs?
Vertebrae in the cervical, thoracic and lumbar regions are separated by intervertebral discs
On the lateral aspect of the column there are ________.
Intervertebral foramina (holes)
What is the function of the intervertebral foramina?
they permit the passage of vessels and nerves into or out of the vertebral canal
Does the spinal cord extend the entire length of the vertebral canal? Why?
No, because of unequal growth rates of the vertebral column and spinal cord
To where does the vertebral column extend in adults and in infants?
In adults it extends from the foramen magnum of the skull to the upper lumbar region (L1- L2) of the vertebral column
In infants it may extend as far as L3
The terminal portion of the spinal cord (found at L1-L2 vertebral levels in adults)
3 connective tissue layers that surround the spinal cord and the brain
What is the thick, outermost layer of the meninges?
The dura mater
What is the middle layer of the meninges, which resembles a spider web?
The arachnoid mater
It is closely associated with the dura mater and lines the dural sac (note – it is not attached to the dura!)
What is the innermost layer of the meninges? (The one closest to the spinal cord)
The pia mater
Epidural (extradural) space
-The area between the dura mater and the vertebral canal.
-Filled with fat and contains the internal vertebral venous plexus.
-Begins at the foramen magnum and ends inferiorly at the sacral hiatus. -Local anesthesia is often injected into the epidural space (epidural block) to anesthetize the nerve roots (e.g. for childbirth).
The dura matter around the spinal cord forms a tube known as the ___.
Dural (thecal) sac (ends at S1-S2)
-Begins at the foramen magnum where it is continuous with the dura mater around the brain.
-Extends approximately to the S2 vertebral level (varies between S1-S3), where it is continuous with the outer part of the external filum terminale (coccygeal ligament) that is anchored to the coccyx.
-Has sleeve-like projections that surround the spinal nerve roots as they exit the vertebral canal.
The subdural space
-Exists between the dura and arachnoid mater
-Is a potential space (i.e. it does not normally contain anything, but could expand if something such as blood leaked into it)
-located between the arachnoid mater and pia mater
-contains cerebrospinal fluid (CSF)
-extends inferiorly as far as the dural sac (S2); therefore, fluid may be sampled from the subarachnoid space without fear of puncturing the spinal cord (access via lumbar puncture)
-is continuous with the subarachnoid space of the brain.
Can the pia mater be separated from the spinal cord?
At the conus medullaris, what happens to a thin strand of the pia mater?
At the conus medullaris, a thin strand of pia mater continues inferiorly as the internal filum terminale, which becomes invested by dura mater at the inferior limit of the dural sac (the pia + dura is called the external filum terminale)
What is the function of the filum terminale?
to anchor the spinal cord and dural sac inferiorly to the coccyx.
Lateral projections of the pia mater that fuse to the dura and help anchor the spinal cord within the vertebral canal.
How many pairs of cranial and spinal nerves are there?
12 cranial (CN I - CN XII)
31 spinal (C1 - C8, T1 - T12, L1 - L5, S1 - S5, C01)
Peripheral nervous system (PNS)
consists of all of the nervous tissue located outside of the CNS - primarily nerves that function as communication links between the body and CNS.
Nerves that connect to the brain are called cranial nerves, and nerves that connect to the spinal cord are spinal nerves.
Cranial nerves primarily innervate the head and the neck. The major exception to this is CN ___
X (vagus nerve); it travels as far as the lower abdomen.
Spinal nerves primarily innervate structures below the head. The exception to this rule is that:
the first few cervical nerves do send some small branches into the head
The spinal nerves are attached to the spinal cord at regular intervals. This is a reflection of what?
Their segmental development
Spinal cord segment
Portion of the spinal cord that is associated with one pair of spinal nerves
Each somite (block of mesoderm) is associated with a spinal cord segment
Spinal cord and spinal nerves have a ______ pattern of development
Segmental; Each spinal cord segment has one pair of spinal nerves attached to it
Somites give rise to:
segments of skin, bone and muscle that are innervated by the spinal nerve pair associated with that particular segment
Segment of skin innervated by a specific pair of spinal nerves
Spinal nerves are connected to the spinal cord by ____
Rootlets, which are collectively known as the dorsal root and the ventral root.
Dorsal (posterior) root
The dorsal (posterior) root is the sensory root – it only contains sensory neurons
The dorsal root has a ganglion associated with it called the dorsal root ganglion (a.k.a. spinal ganglion)
Ventral (anterior) root
the ventral (anterior) root is the motor root and only contains motor neurons
Once the spinal nerve is formed, it divides into two branches. What are they?
1. dorsal ramus: innervates the back
2. ventral ramus: travels around the body wall and innervates the neck, trunk and limbs
"Typical" spinal nerves
Spinal nerves in the thoracic region (specifically T2-T12) are considered to be “typical” spinal nerves because their ventral rami do not form plexuses.
A network or mixing of nerves
Only _____ rami form nerve plexuses.
Which spinal nerves are considered "atypical"
Spinal nerves in the cervical, lumbar and sacral regions (as well as T1) are “atypical” because their ventral rami form nerve plexuses. Some of these plexuses travel out into the extremities (limbs)
How do spinal nerves exit the vertebral column?
Through the intervertebral foramina
The cervical spinal nerves exit the vertebral column (superior/inferior?) to their same numbered vertebra
SUPERIOR; e.g. the C5 nerve passes through the intervertebral foramen between the C4 and C5 vertebrae.
NOTE: Since, there is an eighth cervical nerve but no C8 vertebra, the C8 nerve passes superior to the T1 vertebra and the T1 nerve must pass inferior to the T1 vertebra.
***All the remaining spinal nerves pass inferior to their corresponding vertebra
The distance between a spinal cord segment and its corresponding vertebra _____ as you move inferiorly down the spinal cord
Increases; likewise, the distance the spinal nerve roots must travel to exit the vertebral canal also increases. Both are particularly noticeable in the lumbar and sacral regions of the vertebral column.
The lumbar and sacral spinal nerve roots are seen in kind of a bunch in the inferior part of the vertebral canal as they travel towards their corresponding intervertebral foramina.
This collection of nerve roots is called the cauda equina, due to its resemblance to a “horse’s tail”
Functional unit of the nervous system
The neuron (carries nerve impulses; IS NOT THE SAME THING AS A NERVE). A nerve is a bundle of neurons fibers.
A single neuron = a single nervous system cell. Many neurons are combined to form a fascicle, and many fascicles are combined to form a nerve. Roots also contain many neurons.
Three basic parts of a neuron
1. a cell body that contains organelles
2. a receptive process (dendrite) that carries the impulse towards the cell body
3. a conductive process (axon) that carries the impulse away from the cell body.
Dendrite --> cell body --> axon is the direction the impulse travels
***The term “nerve fiber” is often used interchangeably with “neuron”, however by strict definition “nerve fiber” refers to the axon.
Collection of neuron cell bodies in the CNS
collection of neuron cell bodies in the PNS that are enclosed by a connective tissue covering
Collection of neuron processes (axons) in the CNS
Collection of neuron processes (axons) in the PNS that are enclosed by a connective tissue sheath
have 1 process and are common in invertebrates (not found in humans after birth).
have 2 processes and are only found in a few special locations, e.g. the retina
have 1 process that splits into 2; they are abundant in the PNS
have more than 2 processes and are abundant in both the CNS and PNS.
Neurons are classified by 2 criteria
(1) the direction their impulse is traveling relative to the CNS, and (2) the type of structure they are innervating
conduct impulses towards the CNS (they are typically pseudounipolar)
conduct impulses away from the CNS (they are multipolar)
2 major types of structures that neurons innervate
1. somatic structures
2. visceral structures
-derived from somites
-include skeletal muscle, skin, bones and joints.
-are generally involved with moving and supporting the body – they form the “framework” of the body
-protection, voluntary movement
-parts of the body concerned with involuntary activities
-include organs, glands and blood vessels
-help to maintain homeostasis
-carry out “internal functions” of the body such as digestion, respiration, and excretion
Somatic afferent (GSA)
Afferent impulses from skin, skeletal muscle, bones, ligaments, and tendons (touch, pain, temperature, proprioception)
Somatic efferent (GSE)
Motor impulses to skeletal muscles
Visceral afferent (GVA)
Afferent impulses from organs, glands, mucous membranes, and blood vessels (involved with visceral reflexes)
Visceral efferent (GVE)
Motor impulses to smooth and cardiac muscle. Secretory impulses to glands.
Consists of 2-neuron chain
Autonomic nervous system
Typical thoracic spinal cord
The presence of a lateral horn and relatively thin ventral/dorsal horns are typical of the thoracic spinal cord.”
Spinal nerves develop from ___
Neural crest cells
Central nervous system
the brain and spinal cord