Nervous system 2 Flashcards
What is the myelin-providing glial cells in the CNS?
Oligodendrocytes
What is the myelin-providing glial cells in the PNS?
Schwann cells
What are the collections of cell bodies in the CNS called?
Nuclei (singular nucleus)
What are the collections of cell bodies in the PNS called?
ganglia (singular ganglion)
what are the bundles of axons in the CNS called?
Tracts
what are the bundles of axons in the PNS called?
nerves
what are axons?
long, slender projections of neurons that transmit electrical signals
what are axons responsible for in the PNS?
connecting the CNS to muscles, glands and sensory organs
What do axons in the periphery cluster together to form?
Nerves, which are collections of thousands of individual axons within a common external connective tissue sheath called the epineurium.
What connective tissue sheath surrounds an entire nerve?
The epineurium.
How are axons within a nerve organized?
They are sub-grouped into fascicles.
What connective tissue sheath surrounds each fascicle within a nerve?
The perineurial sheath.
what is the simple pathway of nerves?
sensory neuron (afferent) -> interneuron -> motor neuron (efferent)
What are the two types of peripheral nerve axons based on their function?
Efferent (motor) axons, which carry signals from the CNS, and afferent (sensory) axons, which carry signals to the CNS.
What is the function of efferent axons in the peripheral nervous system?
To carry motor signals from the CNS to the periphery.
What is the function of afferent axons in the peripheral nervous system?
To carry sensory signals from the periphery to the CNS.
How are efferent and afferent axons connected to the CNS?
Through separate spinal roots.
What are the two main types of nerves involved?
Spinal nerves and cranial nerves.
What is the relationship between sensory neurons, interneurons, and motor neurons in this diagram?
Sensory neurons transmit signals from receptor endings to the CNS, interneurons process these signals within the CNS, and motor neurons carry the response signals from the CNS to the muscles or glands.
Through which root do sensory axons enter the CNS?
The dorsal (posterior) root.
How do efferent (motor) and afferent (sensory) axons segregate before entering the CNS?
Sensory axons join the CNS via the dorsal (posterior) root, while motor axons join via the ventral (anterior) root.
Through which root do motor axons connect to the CNS?
The ventral (anterior) root.
where do cell bodies reside in a spinal segment?
dorsal root ganglion (DRG)
What structures of the CNS do the dorsal and ventral roots connect to?
The spinal cord or brainstem.
Why is the segregation of sensory and motor axons important?
It ensures the proper routing of sensory signals to the CNS and motor signals to the periphery.
what are the sections of the white matter?
- dorsal (posterior) column
- ventral (anterior) column
- lateral column
sections of grey matter
- posterior (dorsal) horn
- lateral horn
- anterior (ventral) horn
from back to front what are the sections of a spinal cord segment?
- posterior median sulcus
- central canal (filled with CSF)
- grey commissure
- white commissure
- anterior median fissure
the ventral and dorsal root meet to form what?
the spinal root
what are the small roots called connecting the spinal cord?
rootlets
function of the anterior horn motor neurons
lower motor neurons (LMNs) innervate skeletal muscles to trigger contraction
- efferent pathway
what neurons the motor pathway of the grey matter contain?
preganglionic autonomic neurons
function of the posterior horn sensory input
- afferent pathway
responsible for processing and receiving sensory informations (does not contain LMNs)
process of the posterior horn sensory input
sensory neurons carry sensory neurons from the periphery interneuron relay and process sensory signals
what are the types of myelinated fibers in posterior horn?
Aβ myelinated (touch)
Aδ myelinated fibers (pain)
non-/peptidergic C
Aβ myelinated (touch)
large, heavily myelinated
- very fast transmission
Aδ myelinated fibers (pain)
thinly myelinated, small
non-/peptidergic C
unmyelinated
what are the 31 pairs of spinal nerves
- 8 pairs of cervical nerves (C1-C8)
- 12 pairs of thoracic nerves (T1 – T12)
- 5 pairs of lumbar nerves (L1-L5)
- 5 pairs of sacral nerves (S1-S5)
- 1 pair of coccygeal nerves (Co1)
What are the two branches formed when a spinal nerve divides?
The dorsal (posterior) ramus and the ventral (anterior) ramus.
What area of the body does the dorsal ramus serve?
The dorsal ramus serves the back and associated tissues.
What area of the body does the ventral ramus serve?
The ventral ramus serves the front and sides of the body, including the limbs.
What is the function of the dorsal root in a spinal segment?
The dorsal root carries sensory (afferent) information into the spinal cord.
What is the function of the ventral root in a spinal segment?
The ventral root carries motor (efferent) signals from the spinal cord to the periphery.
What is the role of the white ramus in the sympathetic nervous system?
The white ramus carries myelinated preganglionic sympathetic fibers from the spinal cord to the sympathetic chain.
What is the role of the gray ramus in the sympathetic nervous system?
The gray ramus carries unmyelinated postganglionic sympathetic fibers from the sympathetic chain back to the spinal nerve for peripheral innervation.
What are the two types of matter shown in the spinal cord cross-section, and what are their functions?
- Gray matter: Processes and integrates information; contains neuron cell bodies.
- White matter: Transmits signals up and down the spinal cord; contains myelinated axons.
What is the relationship between the dorsal root and sensory neurons?
The dorsal root contains sensory neurons that transmit signals to the gray matter of the spinal cord.
What is a dermatome?
A dermatome is an area of skin that is mainly supplied by a single spinal nerve.
What is a myotome?
A myotome is the group of muscles that a single spinal nerve innervates.
Why are dermatomes clinically significant?
Dermatomes help identify spinal nerve or spinal cord injuries based on areas of sensory loss or altered sensation.
Why are myotomes clinically significant?
Myotomes help assess motor function and identify spinal nerve or root injuries based on muscle weakness.
What is the difference between the dorsal and ventral rami of a spinal nerve?
- Dorsal rami supply the posterior part of the body, innervating the muscles and skin of the back, and do not form major plexuses.
- Ventral rami serve the anterolateral part of the body (e.g., limbs) and often contribute to nerve plexuses.
What does the dorsal root of a spinal nerve contain?
The dorsal root contains sensory (afferent) fibers that carry signals to the spinal cord.
What does the ventral root of a spinal nerve contain?
The ventral root contains motor (efferent) fibers that carry signals away from the spinal cord to muscles and glands.
What are sympathetic rami, and what is their function?
Sympathetic rami are branches of the spinal nerve that connect to the sympathetic chain, carrying autonomic fibers involved in innervating internal organs.
What is the role of the splanchnic nerve in the autonomic nervous system?
The splanchnic nerve carries autonomic fibers that supply internal organs, specifically contributing to the innervation of visceral structures.
What is a plexus, and which rami contribute to its formation?
A plexus is a cluster of interconnecting nerves. The ventral rami contribute to the formation of major plexuses (e.g., brachial, lumbar plexuses).
Why do the dorsal rami not form major plexuses?
The dorsal rami innervate the muscles and skin of the back and do not require complex nerve interconnections.
How do the ventral rami differ in the thoracic region compared to other regions?
In the thoracic region, ventral rami contribute to the intercostal nerves rather than forming plexuses.
Why can a single spinal nerve injury not always affect a specific region?
Because of overlapping contributions, a single spinal nerve injury may not fully impact a specific area.
What is a peripheral nerve comprised of?
A peripheral nerve often contains fibers from multiple spinal nerves, meaning several spinal segments contribute axons to a single peripheral nerve.
What advantage does the overlapping contribution of spinal nerves provide to peripheral nerves?
It allows a single peripheral nerve to detect signals from multiple regions.
Name the four major nerve plexuses and the regions they innervate.
Cervical plexus: Head, neck, and diaphragm.
Brachial plexus: Upper limbs.
Lumbar plexus: Lower limbs.
Sacral plexus: Lower limbs.
What regions of the body are innervated by the cervical plexus?
The head, neck, and diaphragm.
Which nerve plexus is responsible for innervating the upper limbs?
The brachial plexus.
What is the combined term for the lumbar and sacral plexuses, and what do they innervate?
The lumbosacral plexus, which innervates the lower limbs.
Which plexus is associated with the thoracic region?
The thoracic region does not form major plexuses, as the ventral rami in this region primarily contribute to the intercostal nerves.
How many cranial nerves are there?
There are 12 cranial nerves.
Which cranial nerves are located in the cerebral hemisphere?
The olfactory nerve (I) and the optic nerve (II).
Which cranial nerves are associated with the midbrain?
The oculomotor nerve (III) and the trochlear nerve (IV).
Name the cranial nerves associated with the pons.
The trigeminal nerve (V), abducens nerve (VI), facial nerve (VII), and vestibulocochlear nerve (VIII).
Which cranial nerves originate in the medulla?
The glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI), and hypoglossal nerve (XII).
What is the function of the olfactory nerve (I)?
Sensory; it is responsible for the sense of smell.
What is the primary function of the optic nerve (II)?
Sensory; it transmits visual information from the retina to the brain.
Which muscles are innervated by the oculomotor nerve (III)?
It innervates all the eye muscles except the superior oblique (IV) and the lateral rectus (VI).
What is the function of the trochlear nerve (IV)?
Motor; it controls the superior oblique muscle of the eye.
What does the trigeminal nerve (V) control?
It has sensory fibers for the face, teeth, and sinuses, and motor fibers for the muscles of mastication.
What is the function of the abducens nerve (VI)?
Motor; it controls the lateral rectus muscle of the eye.
Which muscles are controlled by the facial nerve (VII)?
Motor; it controls the muscles of facial expression. It also has sensory functions for the anterior part of the tongue and soft palate.
What is the sensory function of the vestibulocochlear nerve (VIII)?
It provides sensory input for hearing and balance (inner ear).
What is the motor function of the glossopharyngeal nerve (IX)?
It controls pharyngeal musculature.
What is the sensory function of the glossopharyngeal nerve (IX)?
It provides sensory input from the posterior part of the tongue, tonsils, and pharynx.
What are the functions of the vagus nerve (X)?
Motor: Controls the heart, lungs, bronchi, and gastrointestinal tract.
Sensory: Provides input from the heart, lungs, gastrointestinal tract, and external ear.
Which muscles are innervated by the accessory nerve (XI)?
The sternocleidomastoid and trapezius muscles.
What is the function of the hypoglossal nerve (XII)?
Motor; it controls the muscles of the tongue.
Which cranial nerve is responsible for parasympathetic control of organs?
The vagus nerve (X).
Which cranial nerve has both sensory and motor fibers for the face?
The facial nerve (VII).
What sensory inputs are received by the glossopharyngeal nerve (IX)?
Inputs from the posterior tongue, tonsils, and pharynx.
How does the vestibulocochlear nerve (VIII) contribute to balance?
It carries sensory signals from the vestibular apparatus of the inner ear.
Which cranial nerve controls eye movement through the lateral rectus muscle?
The abducens nerve (VI).
what is the types of the autonomic nervous system?
- sympathetic
- parasympathetic
what is the visceral afferent system
internal organs to the CNS, informs the brain
what is the visceral efferent system
- preganglionic neuron (orginates in the CNS)
- postganglionic neuron (extends to target neuron)
what is the somatic afferent system?
- sensory pathways that transmit signals from eg. skin, muscles, joints, bones to the CNS
what is the pathway of the somatic afferent system?
enters through spinal cord via dorsal root of the spinal nerves
what is the pathway of the somatic efferent system?
signals from CNS to the skeletal muscles
features of the somatic motor
- single neuron
- voluntary control
- skeletal muscle
features of the autonomic nervous system
- two neurons (pre/post-ganglionic)
- involuntary
- smooth muscle and glands
what is the autonomic nervous system?
an effector system in the CNS and PNS mediating unconscious homeostatic control of organ and body physiology
what are the two divisions of the autonomic nervous system?
- thoracolumbar outflow
- craniosacral outflow
which outflow does the sympathetic autonomic belong to?
thoracolumbar outflow
what is the autonomic motor pathway
cell bodies within the lateral horn of the spinal cord fibers exit the spinal via the ventral root, then through the white rami and then enter the sympathetic chain ganglia
which outflow does the parasympathetic autonomic belong to?
craniosacral outflow
features of the craniosacral outflow
- originates from the cranial nerves in the brainstem + sacral (S2-S4)
- conserves energy, stimultes digestion etc
- nerve fibers travel through nerves to organs
- fibers from the sacral part innervate organs to lower abdomen + pelvis
features of thoracolumbar outflow
- arises from the thoracic (T1-T2) and lumbar (L1/L2/L3)
- increases heart rate/dilating pupils/redirecting blood flow to the muscles
- nerve exits the spinal cord to the sympathetic ganglia
what is the postganglionic neurons
sends fibers via the grey rami communicates to join spinal nerves and innervate peripheral tissues
what is the preganglionic neurons
- synapse at the same level
- ascend/descend to synapse
- pass through chain without synapse
Where do sympathetic fibers originate?
Sympathetic fibers originate in the thoracolumbar division of the spinal cord, specifically from the T1–L2 spinal cord segments.
Through which structure do preganglionic sympathetic fibers enter the sympathetic trunk?
Preganglionic sympathetic fibers enter the sympathetic trunk through the white rami communicantes.
What are the possible pathways a preganglionic fiber can take after entering the sympathetic trunk?
A preganglionic fiber can take one of the following pathways:
Synapse at the same level:
1. Synapse with a postganglionic neuron in the ganglion at the same level.
- Ascend or descend the trunk: Travel up or down the trunk to synapse in a ganglion at a different level.
- Pass through without synapsing: Travel through the trunk and form splanchnic nerves, synapsing in prevertebral ganglia.
- Direct innervation: Travel directly to the adrenal medulla without synapsing.
What are the white and gray rami communicantes?
- White rami communicantes: Carry preganglionic fibers into the sympathetic trunk.
- Gray rami communicantes: Carry postganglionic fibers out of the sympathetic trunk to join spinal nerves.
What happens when fibers synapse at the same level in the sympathetic trunk?
Postganglionic fibers exit the ganglion via gray rami communicantes and join the corresponding spinal nerve to reach their target tissues.
What happens when fibers ascend or descend the trunk before synapsing?
These fibers synapse in a ganglion at a different level, allowing the sympathetic system to influence areas outside the thoracolumbar region.
What are splanchnic nerves?
Splanchnic nerves are bundles of preganglionic fibers that pass through the sympathetic trunk without synapsing. They synapse in prevertebral ganglia near target organs.
How do sympathetic fibers interact with the adrenal medulla?
Preganglionic fibers travel directly to the adrenal medulla, stimulating it to release adrenaline and noradrenaline into the bloodstream.
Why is the sympathetic trunk important for the sympathetic nervous system?
The sympathetic trunk serves as a distribution hub, allowing sympathetic fibers to ascend, descend, or reach distant organs and tissues efficiently.
What is the origin of the parasympathetic sacral nerves?
The parasympathetic sacral nerves originate from the S2–S4 spinal cord segments.
What are parasympathetic sacral nerves also known as?
They are also known as the pelvic splanchnic nerves.
How do pelvic splanchnic nerves differ from other splanchnic nerves?
Pelvic splanchnic nerves are part of the parasympathetic nervous system, while other splanchnic nerves are generally associated with the sympathetic nervous system.
What organs do the pelvic splanchnic nerves innervate?
They innervate the following:
Pelvic organs: Bladder, rectum, and reproductive organs.
- Lower abdominal organs:
- Distal colon (descending colon and sigmoid colon).
Through which plexuses do pelvic splanchnic nerves distribute their fibers?
They distribute fibers via the inferior hypogastric plexus and other associated pelvic plexuses.
What type of fibers do the pelvic splanchnic nerves carry?
They carry preganglionic parasympathetic fibers to synapse in ganglia near or within the walls of target organs.
What functions do the pelvic splanchnic nerves mediate?
- Bladder: Stimulate contraction of the detrusor muscle and relaxation of the internal urethral sphincter for urination.
- Rectum: Facilitate peristalsis and relaxation of the internal anal sphincter for defecation.
what are the parasympathetic cranial nerves
- oculomotor nerve (III)
- facial nerve (VII)
- glossopharyngeal nerve (IX)
- vagus nerve (X)
what function does the oculomotor nerve (III) have
narrows pupil and focuses lens
what function does the facial nerve (VII) have?
tear, nasal and salivary glands
what function does the glossopharyngeal nerve (IX) have?
parotid salivary gland
what function does the vagus nerve (X) have?
- viscera as far as proximal half of colon
- cardiac, puulmonary, and esophageal plexus
