Comprised of the neuronal cell bodies, nerve fibers, and connective tissues of the brain and spinal cord
Central nervous system (CNS)
Initiates, regulates, and coordinates body functions
CNS
The CNS communicates with other functional components of the body via the
Peripheral nervous system (PNS)
Collections of neuronal cell bodies within the CNS are called
Nuclei
The nerve fibers of the CNS are commonly arranged into discreet bundles called
Tracts
Comprised of the neuronal cell bodies, nerve fibers and connective tissues that lie outside the CNS
-conveys information between CNS and peripheral structures
Peripheral Nervous System (PNS)
Collections of neuronal cell bodies outside of the CNS are referred to as
Ganglia
Comprised of peripheral nervous tissue responsible for
carrying signals to and from skeletal muscles, tendons,
joints and skin
Somatic Nervous System
Conveys sensations of pain, temperature, tough, and proprioception from the periphery to the CNS
Somatic PNS
The cell bodies of lower somatic motor neurons are located in the
Ventral horn of spinal cord
The cell bodies of somatic sensory neurons are located in
Dorsal root (spinal) and cranial nerve ganglia
The internal organs in the main cavities of the body, especially those in the abdomen, e.g., the intestines.
Viscera
Comprised of peripheral nervous tissue responsible for
carrying signals to and from the viscera.
-conveys visceral sensations such as distension
Autonomic PNS
The Autonomic PNS is comprised of
- ) Sympathetic nervous system
2. ) Parasympathetic nervous system
Elicits the so-called “fight or flight” response, which includes pupilary dilation, increased heart rate, blood pressure, and sweating
Sympathetic nervous system
Controls digestive functions, slows the heart rate, and constricts the pupils
Parasympathetic nervous system
Both utilize two motor neurons in the peripheral path to innervate smooth and cardiac muscle
Sympathetic and parasympathetic nervous systems
The anatomic unit of the nervous system
-consists of a cell body, dendrite(s), and an axon
Neuron
Microscopically, neurons can be classified as being
-based on the number of processes associated with their cell body
Multipolar, bipolar, or unipolar
Functionally, neurons are classified as being either
Motor (efferent) or Sensory (afferent)
These neurons are multipolar and carry information away from the CNS
-cell bodies are located in the nuclei, within the ventral horn of spinal cord
Motor (efferent) neurons
These neurons are unipolar and carry information towars the CNS
-cell bodies are clustered in ganglia located outside CNS
Sensory (afferent) Neurons
Ganglia associated with spinal nerves are called
Dorsal root ganglia (spinal ganglia)
Lies within the vertebral canal extending from the foramen magnum to the level of the intervertebral disc between L1/L2 vertebra
Spinal Cord
Surrounded by three meningeal layers: dura mater (outermost), arachnoid mater (intermediate), and pia mater (innermost) and bathed in cerebrospinal fluid (CSF) that fills the subarachnoid space
Spinal cord
The spinal cord consists of
White and grey matter
Bundles of myelinated axons arranged in discreet fiber tracts
White matter
Arranged into three major horns: ventral (motor), dorsal (sensory), and lateral (autonomic motor)
Grey matter
Attach to the spinal cord via ventral (motor) and dorsal
(sensory) roots and functionally divide it into 31 spinal cord segments
Spinal nerves (31 pairs)
There are 31 pairs of spinal nerves, which comprises
8 Cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal
Spinal nerves exit the vertebral canal through intervertebral foramen. Where do the following exit?
- ) Spinal nerves C1-C7
- ) Spinal nerve C8
- ) Thoracic, lumbar, and sacral nerves
- ) Above the vertebrate (I.e. C3 exits above C3 between C2 andC3)
- ) Below C7
- ) Below their corresponding vertebra
Spinal nerves exit the vertebral canal through
Intervertebral foramen
Each spinal nerve is attached to the spinal cord via a
1.) Ventral (motor) root
and a
2.) Dorsal (sensory) root
The ventral root carries only motor nerve fibers and the dorsal root carries only sensory nerve fibers. these roots merge to form the
Mixed (motor and sensory) spinal nerve
The spinal nerve divides into two, forming a
-also mixed nerves
Ventral ramus and dorsal ramus
What three things do dorsal rami innervate?
- ) Skin of back
- ) True back muscles
- ) Zygapophyseal joints
Innervate the remainder of the skin and skeletal muscles of the neck, trunk, and limbs
Ventral rami
The skin of the neck, body wall and limbs is divided up
into segments or slices called
Dermatomes (skin slice)
Each dermatome is innervated by the
Dorsal or ventral rami of spinal nerves
Dermatome segments overlap eachother such that innervation of the ventral T10 dermatomal segment is supplied in part by
T9 and T11 ventral rami
Thus, complete anesthesia of the T10 dermatomal segment would require knocking out the
T9,T10, and T11 ventral rami
The portion of the PNS responsible for monitoring and regulating visceral functions
Autonomic Nervous System
Primarily responsible for motor innervation of smooth muscle lining blood vessels, cardiac muscle and sweat glands and sensory innervation of viscera
Sympathetic ANS
Primarily responsible for motor innervation of smooth muscle lining digestive tract, cardiac muscle and salivary glands and sensory innervation of viscera
Parasympathetic ANS
Distributed with spinal nerves and blood vessels
Sympathetic nerve fibers
Distributed with cranial nerves and pelvic autonomic nerves
Parasympathetic nerve fibers
Both multipolar neurons, which carry signals away from the CNS
Somatic and visceral motor neurons
Innervates skeletal muscle and takes a 1 motor neuron pathway from CNS
Somatic motor
Innervate smooth muscle, modify cardiac muscle and glands, and takes a 2 motor neuron pathway from CNS
Visceral motor
A single neuron pathway from CNS to skeletal muscle. Cell bodies are multipolar and located in the ventral (motor) horn of the spinal cord
Somatic Motor (efferent)
For visceral motors, cell bodies of the first motor neuron (preganglionic) are located in the
CNS
For visceral motors, cell bodies of the second motor neuron (post ganglionic) are located in the
Ganglia in PNS
Preganglionic neurons innervate ONLY
Post ganglionic neurons (directly innervates visceral structures)
Sympathetic and parasympathetic motor innervation of smooth muscle, cardiac muscle and glands both
require a two neuron pathway with the first neuron located in the CNS and the second neuron in the
PNS
Where are the preganglionic bodies of sympathetic motors located?
-referred to as thoracolumbar outflow
Lateral horn of T1-L2
Where are the postganglionic cell bodies of sympathetic motors located?
Paravertebral and prevertebral ganglia
Where are the preganglionic bodies of parasympathetic motors located?
-craniosacral outflow
Brainstem nuclei and lateral horn of spinal cord segments S2-S4
Where are the postganglionic cell bodies of parasympathetic motors located?
4 discrete ganglia of the head and enteric ganglia of the gut
Which has a more limited distribution, the parasympathetic or sympathetic system?
Parasympathetic
Does not innervate smooth muscle or glands associated with somatic structures and is therefore not distributed to the trunk or limbs
Parasympathetic system
Distributed throughout the entire body
Sympathetic neurons
Before being distributed, all preganglionic sympathetic fibers enter paravertebral ganglia from T1-L2 via
White rami communicans
The location of sympathetic preganglionic cell bodies found only from T1-L2 spinal cord segments
Lateral horn
Carries preganglionic sympathetic motor axons to spinal nerve
-also carries somatic motor axons
Ventral root
All carry somatic motor axons, somatic sensory fibers, and postganglionic sympathetic axons
Spinal nerves
Carry all of those fibers plus visceral sensory and
preganglionic sympathetic axons
Spinal nerves from T1-L2
Carries pre- and postganglionic sympathetic axons
-Carries somatic motor and sensory fibers and visceral sensory fibers
Ventral Ramus
Connects ventral rami of spinal nerves T1-L2 with paravertebral ganglia, and carries preganglionic sympathetic axons
White ramus communicans
Connects ventral rami of all spinal nerves with paravertebral ganglia, and carries postganglionic sympathetic axons that are distributed to somatic structures
Gray Ramus Communicans
Sympathetic chain of ganglia located alongside the vertebral column
-contain postganglionic cell bodies
Paravertebral ganglia
Connects paravertebral and prevertebral ganglia and carries preganglionic sympathetic axons
-also carries visceral sensory fibers
Splanchnic Nerve
Contain postganglionic cell bodies whose axons are distributed to abdominopelvic viscera
Prevertebral ganglia
Spinal nerves T1-L2 provide innervation primarily to the
Trunk
The blood vessels and sweat glands associated with the trunk are innervated by
-travel in the rami of T1-L2 spinal nerves
Postganglionic sympathetic nerve fibers
Provide innervation to the upper limb
Spinal nerves C5-T1
Provide innervation to the lower limb
L2-S4
The blood vessels and sweat glands associated with the limbs are innervated by postganglionic sympathetic nerve fibers that travel in the
Rami of the spinal nerves
The upper and lower limb spinal nerves (besides T1 and L2) do not have
Preganglionic cell bodies or white rami communicates
The lack of white rami communicates means that there is no direct entry to the
Paravertebral ganglia
Neurons that convey somatic sensations are anatomically identical to those neurons that convey visceral sensations. Both are unipolar neurons with cell bodies located in a
Ganglion
Innervates skin, muscle, and joints and conveys pain, temperature, touch, and proprioception
Somatic sensory neurons
What is the location of the cell bodies of somatic sensory neurons?
Dorsal root ganglia from C2-Co
The somatic sensory neurons take the same pathway as the motor pathway up to the spinal nerve. Then it follows the
Dorsal root to the dorsal horn
Innervates viscera, glands, and blood vessels and conveys distension, nausea, and hunger
Visceral sensory neurons
What is the location of the cell bodies of visceral sensory neurons
Dorsal root ganglia from T1-L2
Visceral sensory neurons follow the same pathway as the motor pathway up till the spinal nerve. Then they follow the dorsal root to the
Dorsal horn
How many neurons do the following require?
- ) Somatic and visceral motor pathway
- ) Somatic and visceral sensory pathway
- ) 2
2. ) 1
Somatic sensory and visceral sensory are both part of the
Autonomic Sensory (afferent) innervation
Convey some pain, but are mostly involved with visceral reflexes such as monitoring blood pressure
Parasympathetic afferent fibers
Travel in cranial nerves and pelvic splanchnic nerves along with visceral efferent fibers
Parasympathetic afferent fibers
Parasympathetic afferent cell bodies are located in the cranial nerve sensory ganglia and dorsal root ganglia of spinal nerves
S2-S4
Go from a stimulus back to the spinal cord
Afferent Nerve
Go from the spinal cord to a body part
Efferent Nerve
Occurs because visceral afferent fibers synapse on the same neurons in the dorsal horn of spinal cord segments T1-L2 as the somatic afferent fibers
Referred pain