nervous system Flashcards
components of CNS vs PNS
Central nervous system- brain and the spinal cord
Peripheral nervous system- nerves and structures that connect the CNS to all parts of the body
SNS vs ANS
Somatic nervous system- refers to that part of the nervous system that predominantly regulates muscular function
Autonomic nervous system- refers to that part of the nervous system that regulates visceral and some special functions
what can the ANS be further divided into?
sympathetic and parasympathetic nervous systems
what are the functions of the NS mediated by?
different types of cells present within the brain and spinal cord and other structures such as ganglia
what are the two types of NS cells ?
neurons
glial cells
how do neurons communicate?
synapses
describe the basic functional unit of a neuron
contains a cell body with a nucleus – called ‘perikaryon’
what are the two process of neurons?
dendrite and axon
describe dendrite
- Transmits impulses towards the cell body
- Generally, there are multiple dendrites
describe the axon
- Transmits impulses away from the cell body
- Always originates as a single process from the cell body
- May divide in multiple processes after
travelling a distance from its origin
what are the three types of neurons based on its process and define them
Unipolar (Pseudounipolar):
The dendrite and axon come together to form a single process to the cell body. These neurons are also called ‘pseudounipolar’.
Bipolar:
The dendrites join together to form a common trunk before they reach the cell body at a site that is different from that of the origin of the axon.
Multipolar:
A number of dendrites join the cell body at different points. Most neurons are multipolar.
how do neurons communicate with each other?
through the formation of synapses and they transmit information in the form of action potentials.
what are synapses?
communication between one neuronal membrane to another
how does communication via synapses occur?
through the transmission of signals which could be either electrical or chemical in nature
define axosomatic
connection between an axon of one neuron and a cell body of another neuron
define axodendritic
connection between an axon of one neuron and a dendrite of another neuron
define axoaxonic
between an axon of one neuron and an axon of another neuron
what is the difference between nuclei and ganglia?
nuclei- Neuronal aggregations in the brain
ganglia- aggregations of cell bodies in the peripheral nerves
what are glia and the 3 types?
- provide nutrition to neurons and help with ‘neurotransmission’.
- do not directly participate in neurotransmission.
- produce myelin which surrounds nerve fibers and provide insulation, protection and support
- 3 types: astrocytes, oligodendrocytes, microglia
describe astrocytes
- star-shaped
- found in the brain and spinal cord
- histologically identified by the presence of a protein called ‘glial fibrillary acidic protein (GFAP)’
- ## involved in various functions that are critical for CNS function: metabolic support for neurons, maintenance of blood-brain barrier, repair of injury to the nervous system, regulating ion concentrations, etc.
describe oligodendrocytes
provide support to axons of the CNS by producing myelin sheath.
describe microglia
- cells of immune origin and are very critical for the immune defence mechanism of the CNS
- several types have the ability to undergo changes in their structure to enable them to participate in immune functions in the CNS.
what is the spinal cord?
- cylindrical structure that runs between the hindbrain to the lumbar vertebrae
what are the fibre tracts (which matter) of the spinal cord?
- white matter
- carry information to and from the brain
what are cell bodies (which matter) of the spinal cord?
- grey matter
- either interneurons or motor neurons that give rise to motor fibres
___________(dorsal and ventral) emerge from the spinal cord on each side and merge to form the spinal nerves
nerve roots
what fibres do the spinal nerves contain?
sensory and motor
where are sensory neurons (cell bodies) for the spinal cord located?
dorsal root ganglion
describe the process of how the spinal cord and its nerves provide innervation to muscles
- sensory neurons located in dorsal root ganglion
- dendrites carry the sensory information from the periphery to the cell body and then through the axons (dorsal root) towards the dorsal horn of the spinal cord (afferent – towards the spinal cord)
- Motor neurons are typically located in the ventral horn of the spinal cord and their axons travel through the ventral root (efferent – away from the spinal cord) and join the dorsal roots to form the spinal nerve
- spinal nerve exits through the intervertebral foramen, and splits into dorsal and ventral branches and provides innervation to muscles.
what segments are the spinal cord divided into?
Cervical, Thoracic, Lumbar, Sacral, and Caudal
name and describe the two enlargements along the length of the spinal cord
i) cervicothoracic area (between last three or four cervical spinal cord segments and first two or three thoracic segments)
ii) lumbosacral area (between last three lumbar spinal cord segments and first two sacral segments)
what does the cervicothoracic area and lumbosacral area give rise to?
brachial and lumbosacral plexus
what is the difference between the brachial and lumbosacral plexus?
- brachial plexus gives rise to nerves that innervate the forelimb
- lumbosacral plexus gives rise to nerves that innervate the hind limb
what are the gross divisions of the brain?
- hindbrain (rhombencephalon = Metencephalon “pons”+ Myelencephalon “medulla oblongata”) (metencephalon “cerebellum”)
- midbrain (Mesencephalon)
- forebrain (Diencephalon+Telencephalon)
describe the cerebellum, the structure that separates the hemispheres, and the term for the narrow middle portion
- globular mass of neural tissue connected to the brain stem by three peduncles
- separated from the cerebral hemispheres by a transverse fissure and is physically separated by ‘tentorium cerebelli’
- consists of two lateral hemispheres and a narrow middle portion (median ridge) called ‘vermis’
what is the purpose of the cerebellum?
controls balance and is responsible for coordinating postural and locomotor activities
describe the midbrain
- known as mesencephalon
- made of crura cerebri, tectum, tegmentum and cerebral peduncle
what is the forebrain comprised of?
diencephalon and the telencephalon
what is the most ventral part of the diencephalon?
hypothalamus
what are the components of diencephalon?
hypothalamus
thalamus
epithalamus
what does the epithalamus include?
pineal gland
what is the function of the thalamus?
relay and integration center of the brain.
how is the telencephalon formed?
two cerebral hemispheres.
what are the three specific types of innervations of the cranial nerves?
- Nerves, that are responsible for special senses
- Nerves that provide innervation to head muscles
- Nerves, that provide innervation to structures that originate from the pharyngeal arch
olfactory nerves (CN I)
- Fibers of the olfactory nerves pierce through the cribriform plate of the ethmoid bone of the nasal cavity.
- cell bodies of these fibers are located in the olfactory bulb of the brain
optic nerve (CN II)
- responsible for vision
- arises from diencephalon and connects the diencephalon with the retina of the eye
- optic tracts decussate (cross over) at the optic chiasm
- optic nerve exits through the optic foramen in the skull.
occulomotor nerve (CN III)
- contains both somatic and autonomic fibers (visceral efferent – parasympathetic)
- Occulomotor nerve exits from the midbrain
- somatic component of the occulomotor nerve provides motor innervation to some of the muscles of the eyeball
trochlear nerve (CN IV)
- arises from the midbrain and innervates the dorsal oblique muscle of the eyeball and exits through the orbital fissure of the skull
trigeminal nerve (CN V)
- largest sensory nerve among the cranial nerves
- provides motor innervation to muscles of mandibular origin
- 3 divisions: Ophthalmic, Maxillary, Mandibular
- mandibular nerve exits through the oval foramen of the skull
- ophthalmic and maxillary divisions exit through the orbital fissure and round foramen of the skull
abducent nerve (CN VI)
- arises from the caudal brainstem and exits the skull through the orbital fissure
- innervates the lateral rectus and retractor bulbi muscles of the eyeball
facial nerve (CN VII)
- originates from the brain stem and exits the skull through the stylomastoid foramen
- parasympathetic component
- somatic component of this nerve provides innervation to muscles of facial expression
vestibulocochlear nerve (CN VIII)
- nerve originates from the brain stem
- responsible for the special senses related to vestibular (location and movement perception functions of the ear) and cochlear ( auditory part of the ear) function.
glossopharyngeal nerve (CN XI)
- originates from the brainstem
- parasympathetic and somatic sensory and motor components
- provides sensory innervation to the mucosa of the tongue and the pharyngeal regions
- also provides some motor innervation to the pharyngeal region
vagus nerve (CN X)
- contains visceral afferent, parasympathetic and somatic efferent (motor) fibers
- provides parasympathetic innervation to visceral organs in the thoracic and abdominal area
- Most of the fibers in vagus provide afferent information from the viscera to the brain
- small motor component is responsible for providing innervation to the laryngeal muscles
accessory nerve (CN XI)
- originates from the brain stem and divides into dorsal and ventral branches
- dorsal branch provides innervation to muscles in the neck
- ventral branch innervates sternocephalicus
hypoglossal nerve (CN XII)
- arises from the brain stem and exits the skull through hypoglossal canal
- provides motor innervation to muscles of the tongue
list what the components are of the somatic nervous system
Nerves to skeletal muscle from the spinal cord – contain both sensory and motor fibers (Soma – body)
what is the purpose of the somatic nervous system
Regulates voluntary (movement) and involuntary (reflex) functions
which NS has only one neuron between the central nervous system and the target tissue (skeletal muscle)
Somatic NS
what is the Somatic NS response by target tissue?
contraction (excitation of somatic motor neurons)
where does the Somatic NS originate from
all levels of spinal cord (&brain)
epaxial vs hypaxial muscles
epaxial: muscles located dorsal to transverse axis of vertebrae
hypaxial: muscles located ventral of the transverse axis of vertebrae: includes diaphragm, muscles of the thorax, abdomen, limbs
where does the visceral NS have its sensory and motor components?
to the viscera
what is the purpose of visceral afferents
inform the brain of sensory input from the viscera
what is special about the visceral NS about efferent nerves in comparison to the Somatic NS?
Unlike the somatic nervous system, in the visceral nervous system, efferent nerves have two neurons and either excite or inhibit visceral organ functions which require differential regulation with the sympathetic and parasympathetic system: autonomic NS
what is the purpose of the VNS
Regulates involuntary (reflex) functions
which NS has two neurons between the central nervous system and the target tissues – preganglionic and postganglionic
VNS
what is the VNS response by target tissue?
excitation & inhibition
what are the two types of efferent neurons received by the VNS?
(sympathetic and parasympathetic) -physiologically antagonistic to each other
where does the VNS originate from?
thoracolumbar segments of the spinal cord (sympathetic) and sacral segments of the spinal cord and the brain (parasympathetic)
where are the cell bodies that regulate the ANS?
autonomic nucleus (lateral horn of the spinal cord)
Those located in the thoracolumbar segments of the spinal cord belong to the ________ nervous system.
sympathetic
what is the purpose of the thoracolumbar segments?
connect with cell bodies located along the sympathetic chain in sympathetic ganglia
Cell bodies associated with the parasympathetic nervous system are located in the ____ as well as the ____ ________ of the spinal cord
brain
sacral segments
which cranial nerves have parasympathetic components?
CN III, VII, IX, and X
what is the purpose of the sacral segments?
connect with cell bodies located in terminal ganglia that lie within the target tissues
what is the sympathetic NS made of?
thoraco-lumbar segments.
which system is responsible for the fight or flight reponse?
sympathetic NS
sympathetic NS fibers
Preganglionic fibers are short and post-ganglionic fibers are long
what are the discernable sympathetic ganglia
Cranial cervical ganglion, cervicothoracic and middle cervical ganglion.
where does the parasympathetic NS originate?
from the parasympathetic nuclei of the brain or the intermediate grey matter of sacral spinal cord
what does the parasympathetic NS promote?
stable physiological environment
parasympathetic NS fibers
Preganglionic fibers are long and postganglionic fibers are short
which parasympathetic fibers unite to form the pelvic nerve and provide innervation to pelvic organs and regulates defecation, urination and copulation
S1-S3
which are the cranial nerves of the parasympathetic nerves?
CN III, VII, XI and X
list what the sympathetic NS dilates and constricts
dilates: airways, coronary, skeletal muscle, pupils
constricts: GI sphincters and to skin, stimulates adrenal gland, vasoconstrict of male sex organs (ejaculation)
increases heart rate
inhibits GI secretion and motility,and reduced salivation
stimulates adrenal gland
list what the parasympathetic NS dilates and constricts
constricts: airways, bladder to empty, coronary, skeletal muscle, pupil
stimulates secretion of salivary glands and GI motility
decreases heart rate
vasodilation of male sex organs, erection
