Nervous System III: Spinal Cord, Nerves, ANS Flashcards
The spinal cord is contained within the ______ ______. It extends from the ______
vertebral column
base of the skull (foramen magnum) to the 1st & 2nd lumbar vertebrae (L1-L2) (ends just below the ribs)
The end of the spinal cord is called the _____ _______ (found b/t L1-L2)
conus medullaris
The spinal cord is divided into 4 main segments:
cervical, thoracic, lumbar, & sacral (with a tiny coccygeal part at the very end)
The cervical & lumbar segments are the largest in size & are often referred to as the _____ & _______ _______
cervical
lumbar enlargement
The spinal cord is contained within a _____ ____ that extends from the foramen magnum to the 2nd sacral vertebra (S2). The sac also contains the nerves attached to the spinal cord.
dural sac
What is the diff. from meninges in skull?
the dura is not attached to the vertebrae
Instead, there is an ____ ____ (b/t the dura & vertebrae) that contains fat, connective tissue & veins (different from the skull!)
epidural space
The ______ is attached to the dura & ends at S2 (with the dura)
arachnoid (like how it is in skull)
The __________ _____ b/t the arachnoid & pia is filled with CSF
subarachnoid space
The subarachnoid space is enlarged b/t L1-2 & S2, & is called the _____ _____
lumbar cistern
The cistern is used for…
obtaining CSF samples (lumbar puncture) and spinal anesthesia.
The __ _____ is attached to the spinal cord and sends lateral projections called _______ to the dura (suspends the spinal cord within the dural sac). A strand of pia called the _____ ______ extends from the conus medullaris to the base of the dural sac.
pia mater
denticulate ligaments
filum terminale
The spinal cord consists of a butterfly-shaped core of ___ ____ (mainly neuronal cell bodies and glia) that is surrounded by _____ ____ (ascending and descending axons).
gray matter
white matter
It also has a small ____ ____ that contains CSF.
central canal
The gray matter consists of a ____ ___ and a _____ ____.
dorsal horn
ventral horn
The shape and amount of ____ ____ varies from region to region.
gray matter
It is most plentiful in the cervical and lumbar regions.
The ____ ____ __ ____: it contains interneurons and projection neurons that process and relay sensory information to the brain via ascending tracts.
dorsal horn is sensory
Sensory information enters the dorsal horn from the periphery via the ____ ____, which contains _____ ____.
dorsal root
afferent fibres
(skin has been “affected” by something, therefore “afferent”)
The cell bodies of the sensory neurons that form the dorsal root are located in the _____ _____ ____ (DRG).
dorsal root ganglia
The ____ ___ ___ ____: it contains large motor neurons that project to muscle via _____ _____ in the _____ ____.
ventral horn is motor
efferent fibres
ventral root
Ventral horn motor neurons are innervated by…
descending white matter tracts that originate in the brain.
The white matter consists of…
myelinated axons (fibres) and glia (oligodendrocytes)
The axons are arranged in ____ that have a similar origin, termination, and function (sensory or motor).
tracts
(never a mix)
The major tracts are:
Corticospinal tract, Spinothalamic tract, & Dorsal columns
Corticospinal tract -
descending motor axons that originate in the motor cortex.
Spinothalamic tract -
ascending sensory axons that originate in the dorsal horn.
Dorsal columns –
ascending sensory axons from DRG neurons.
Corticospinal tract (motor):
voluntary movement.
Spinothalamic tract (sensory):
pain and temperature.
Dorsal columns (sensory):
discriminative touch, vibration, proprioception.
Describe the spinal cord: tracts
The motor and sensory information carried in the tracts crosses from one side of the CNS to the other (ie. the right side of the brain controls the left side of the body).
Sensory fibres
are added to sensory pathways as they ascend through the spinal cord. (get bigger as they go through)
Motor fibres
exit the corticospinal tract as they descend through the spinal cord. (smaller as they move through)
Therefore the white matter is most abundant in the cervical region and it…
decreases as you move down through the spinal cord.
The spinal nerves (and cranial nerves) form the…
peripheral nervous system (PNS).
There are 31 pairs of spinal nerves, which are attached to the…
spinal cord.
Spinal nerves are named according to…
the region of the spinal cord that they originate from.
There are __ pairs of cervical nerves, __ thoracic, __ lumbar, __ sacral and __ coccygeal.
8 pairs of cervical nerves, 12 thoracic, 5 lumbar, 5 sacral
1 coccygeal.
The lumbar and sacral nerves are found within the lumbar cistern and are referred to as the _____ _____.
cauda equina. (looks like a horse tail)
Each nerve is attached to the spinal cord by the…
ventral root and dorsal root.
The roots are formed by…
several rootlets.
The dorsal and ventral roots pass through the _______ ______, where they join and form the spinal nerve, which is a mixed nerve - _____ _____ ______.
intervertebral foramina
sensory and motor
(ONLY roots are distinct in function)
After exiting the vertebral column, the nerve splits into an ____ _____ and a shorter ______ _____.
anterior ramus
posterior ramus
The ____ ____ (motor and sensory) innervates the lateral and anterior portions of the body.
anterior ramus (larger & dominant)
The _____ _____ (motor and sensory) innervates the muscles and skin of the back.
posterior ramus (smaller)
The anterior ramus & the posterior ramus innervates the muscles and skin of the back. Together, they supply the _______ and _______ of the body.
myotomes
dermatomes
Myotome:
refers to the muscles innervated by the motor fibres of a single spinal nerve.
Dermatome:
the area of skin innervated by the sensory fibres of a single spinal nerve.
The _____ _____ _____ is a functional division of the PNS.
somatic nervous system
- not necessarily anatomical
The somatic nervous system is characterized by ______ sensation and ________ control of the body.
conscious
conscious
______ ______ ______ (___) is another functional division of the PNS.
Autonomic Nervous System (ANS)
Think “autonomous” or “automatic”.
The autonomic nervous system is characterized by __________ control.
unconscious/involuntary
Innervates the organs and is therefore sometimes referred to as the _____ _______ ______.
visceral nervous system
It is important for regulating homeostasis (ie., body temperature, blood pressure).
Autonomic Nervous System (ANS) is…
Like the somatic nervous system, the ANS has motor and sensory components.
Autonomic Nervous System (ANS)
Sensory component is sometimes referred to as…
VISCERAL AFFERENTS or VISCERAL SENSORY FIBRES.
Autonomic Nervous System (ANS)
Responds to stimuli such as…
stretch, pressure, ischemia (lack of BF), and inflammation.
Autonomic Nervous System (ANS) is involved in…
reflex arcs that are important for regulating ANS activity.
Autonomic Nervous System (ANS) is a motor component & innervates the following target tissues:
- Cardiac muscle
- Smooth muscle (within the walls of blood vessels, G.I. tract, urogenital tract, and respiratory tract)
- Glands (salivary, sweat, adrenal medulla)
What is in general about the ANS?
In general, little conscious control (although there can be conscious influences on ANS activity).
- mind over matter exercises
Why is the ANS important?
It is critical for regulating MANY SYSTEMS including:
1. Cardiovascular System
2. Respiratory System
3. Gastrointestinal System (bowel)
4. Urinary System (bladder)
5. Reproductive System
- Disorders involving the ANS are relatively common. (ex: heart arrhythmia’s, erectile dysfunction, etc.)
- Some of the MOST widely prescribed drugs target the ANS (ie., drugs for hypertension, asthma).
Sensory component (afferent) of the ANS:
1 neuron projecting from a target tissue to the CNS (cell body in dorsal root ganglion).
Motor component (efferent) of the ANS:
• A 2-neuron chain connects the CNS to the target tissue.
• The synaptic connection between the 2 neurons occurs within an AUTONOMIC GANGLION.
• The cell body of the 1st neuron is in the CNS and is referred to as the PRE-GANGLION NEURON; it projects to a ganglion via a MYELINATION axon.
• The cell body of the 2nd neuron is found in the ganglion and is called the POST-GANGLION NEURON, which projects to the target tissue via a NON-MYELINATED AXON.
The synaptic connection between the 2 neurons occurs within an…
autonomic ganglion.
The cell body of the 1st neuron is in the CNS and is referred to as the ______ ____; it projects to a ganglion via a _____ _____.
pre-ganglionic neuron
myelinated axon
The cell body of the 2nd neuron is found in the ganglion and is called the _______ ____, which projects to the target tissue via a ________ ___.
post-ganglionic neuron
non-myelinated axon
The efferent/motor component of the ANS is divided into the:
- Sympathetic Nervous System
- Parasympathetic Nervous System
- A target tissue (ie. heart, G.I. tract) can be innervated by both divisions.
Sympathetic NS
PRE-GANGLIONIC neurons are located in the _________________ (T1 to L2).
thoracic and lumbar segments of the spinal cord
The sympathetic NS is therefore referred to as having _______ output/origin.
thoracolumbar
Axons exit the spinal cord via the ventral root and project to post-ganglionic neurons.
POST-GANGLIONIC neurons are located in the _______ ganglia and ________ ganglia.
paravertebral
prevertebral
Functions of the Sympathetic NS
Activated during the “fight or flight” response:
• Increases heart rate and blood pressure.
• Increases diameter of airways (bronchodilation).
• Inhibits salivary glands (mouth = dry) and decreases G.I. motility (directs blood away from G.I. tract).
• Stimulates adrenal gland.
• Activates sweat glands .
• Dilates pupil. (allow as much light as possible)
Parasympathetic NS
Pre-ganglionic neurons are located in the ______________ and ____________.
brainstem (cranial nerves III, VII, IX, and X)
sacral levels of the spinal cord (S2-4)
The parasympathetic NS is therefore referred to as having ________ output/origin.
craniosacral
Pre-ganglionic axons project to…
parasympathetic ganglia - small and numerous.
Parasympathetic Ganglia are located within or near the…
target tissue (axons of post-ganglionic neurons are short).
Cranial nerves:
innervate the eye, glands of the head, viscera of thorax (heart & lungs) and abdomen (stomach, intestines, liver).
S2-4:
innervate the pelvic viscera (distal colon, bladder, and reproductive organs).
(of PNS)
Functions of the Parasympathetic NS
Active when at rest – “Rest & Digest”.
• Decreases heart rate and blood pressure.
• Decreases diameter of airways (bronchoconstriction).
• Stimulates salivary glands and increases G.I. motility. (help more food through)
• Constricts pupil. (less light)
ANS Functions
• Generally, the sympathetic & parasympathetic NS are generally antagonistic.
• If both innervate a smooth muscle, one division will cause contraction, while the other causes relaxation.
• Together, they determine the overall secretion from a gland or contractile activity of a smooth muscle.
• Sweat glands and the smooth muscle of blood vessels are only innervated by the sympathetic NS.
________ are ONLY innervated by the sympathetic NS.
Sweat glands and the smooth muscle of blood vessels
Regulation of ANS function by the CNS
• Activity of the ANS is largely controlled by the HYPOTHALAMUS (diencephalon).
• The hypothalamus sends projections to the brainstem and spinal cord and thereby regulates the activity of pre-ganglionic sympathetic and parasympathetic neurons.
• The hypothalamus also regulates the strength of autonomic reflexes and coordinates activity of the sympathetic and parasympathetic NS (bowel and bladder function).
Activity of the ANS is largely controlled by the _______ (diencephalon).
hypothalamus
