Module 2: The Nervous System Flashcards
The Nervous System
Coordinates both voluntary and involuntary activities of various systems of the body.
Broadly divided into 2 major systems = Central nervous system and Peripheral nervous system
Central nervous system (CNS)
Includes the brain and spinal cord
Peripheral nervous system (PNS)
Consists of nerves and structures (with some exceptions) that connect the CNS to all parts of the body
What is another way that the nervous systems can be classified by?
Classification based on the nervous system’s innovations and regulations of somatic and visceral structures→ Somatic nervous system (SNS) and Autonomic nervous system (ANS)
Somatic → “soma”
Refers to body
Visceral
Refers to organs
Somatic nervous system (SNS)
Mostly regulates muscular function
Autonomic nervous system
Regulates visceral (organ) and some special functions
Further divided into Sympathetic and Parasympathetic nervous systems
How are the functions of the nervous system brought about, or mediated?
Mediated by different types of cells within the brain and spinal cord and other structures such as ganglia
Types of cells within the nervous system
2 broad types = neurons and glial cells
Neuron(s)
- A basic functional unit of the nervous system
- Mostly communicate with other cells via synapses
- Contains a cell body with a nucleus → “perikaryon”
- Two types of “processes” (finger-like projections from the cell body that can conduct and transmit signals)→Dendrite and Axon
Dendrite
- Transmits impulses aka signals towards the cell body
- There are generally multiple dendrites
Axon
- Transmits impulses aka signals away from the all body
- Always starts as a singular process from the cell body → may divide into multiple processes after traveling a distance from its origin
Types of neurons
3 types → based on the structure of the neuron’s processes
1. Unipolar (aka Pseudounipolar) 2. Bipolar 3. Multipolar
Unipolar aka Pseudounipolar neuron
Dendrite and axon combine into a single process toward the cell body
Bipolar neuron
Dendrites join together as a common trunk before reaching the cell body at a different site than the origin site of the axon
Multipolar neuron
A number of dendrites join the cell body at different points. Most neurons are multipolar
How does a neuron communicate with another neuron, aka communication between neurons?
Neurons communicate with each other via the formation of synapses and they transmit info in the form of action potentials a
Synapses= communicationi between one neuronal membrane to another
Communication is via transmission of signals that can be chemical or electrical signals.
Types of connections (synapses)
Axosomatic vs. Axodendritic vs. Axoaxonic
Axosomatic synapse
Connection between an axon of one neuron and a cell body of another neuron
Axodendritic synapse
Connection between an axon of one neuron and a dendrite of another neuron
Axoaxonic synapse
Connection between an axon of one neuron and an axon of another neuron
Neuronal aggregations
Aggregations of cell bodies
Nuclei
Aggregations of cell bodies in the brain
Ganglia
Aggregations of cell bodies in the peripheral nerves
Glia aka glial cells
Cells that support neurons by providing nutrition to neurons and help with “neurotransmission” → they do not directly participate in neurotransmission
These cells produce “myelin”
Myelin
Surrounds nerve fibers and provide insulation, protection, and support
Produced by glial cells
Types of glia
3 types of glial cells in the CNS: astrocytes, oligodendrocytes, and microglia → a general classification)
Astrocytes
Typically star-shaped
Found in the brain and spinal cord
Identified by the presence of “glial fibrillary acidic protein” (GFAP)
Involved in multivarions functions that are critical for CNS function → includes: metabolic support for neurons, maintenance of blood-brain barrier, repair of injury to the nervous system, regulating ion concentrations, etc.
Oligodendrocytes
Mainly provide support to axons of the CNS by producing myelin sheath.
Microglia
Cells of immune origin → very critical for the CNS’s immune defense mechanism
Several types → have the ability to make structural changes to enable them to participate in immune functions of the CNS
Structure of the Spinal Cord (CNS)
Spinal cord = cylindrical structure running between the hindbrain to the lumbar vertebrae
Contains fibre tracts (white matter) and cell bodies (grey matter)
Dorsal and ventral nerve roots emerge from the spinal cord on each side → merge to form the spinal nerves = contain both sensory and motor fibres
White matter
Fibre tracts that carry information to and from the brain
Grey matter
Cell bodies that are either interneurons or motor neurons that give rise to motor fibres
Sensory neurons (cell bodies) for the spinal cord
Generally located in the dorsal root ganglion
Their dendrites carry the sensory info from the periphery to the cell body → then through the axons (dorsal root) towards the dorsal horn of the spinal cord = afferent aka towards the spinal cord
Motor neurons of the spinal card
Typically located in the ventral horn of spinal cord
Their axons travel through the ventral root = efferent aka away from the spinalcord → and join the dorsal roots, forming the spinal nerve
The spinal nerve exits via the intervertebral foramen (an opening between 2 vertebrae)→ splits into dorsal and ventral branches → provides innervation to muscles
Spinal cord segments
Divided into: Cervical, Thoracic, Lumbar, Sacral, and Caudal
Cross-section of the spinal cord is very similar among the segments
Enlargements along the length of the spinal cord
There are 2 enlargements = the cervicothoracic and lumbosacral areas
These enlargements give rise to the brachial and lumbosacral plexus respectively
Cervicothoracic area
Between the last 3 or 4 cervical spinal card segments and the first 2 or 3 thoracic segments
This enlargement gives rise to the brachial plexus
Lumbosacral area
Between the last 3 lumbar spinal cord segments and the first 2 sacral segments
This enlargement gives rise to the lumbosacral plexus
Brachial plexus
Gives rise to nerves that innervates the forelimb (and other areas)
Lumbosacral plexus
Gives rise to nerves that innervates the hindlimb (and other areas)
Anatomical structure of the brain (CNS)
3 gross divisions: 1. Hindbrain (rhombencephalon = metencephalon + myelencephelon), 2. Midbrain (mesencephalon), 3. Forebrain ( diencephalon + telencephalon)
Hindbrain aka rhombencephalon
Consists of the medulla oblongata aka myelencephaton; the pons aka ventral mesencephalon; the cerebellum aka dorsal mesencephalon
Medulla oblongata aka myelencephalon
Causally continues as the spinal cord
Cerebellum aka dorsal metencephalon
A globular mass of neural tissue connected to the brain stem by 3 peduncles
It is separated from the cerebral hemisphere by a transverse fissures →physicallyseparated by “tentorium cerebelli”
Consists of 2 lateral hemispheres and a narrow middle portion (aka median ridge) called “vermis”
Role: controls balance and is responsible for coordinating postural and locomotor activities
Midbrain aka mesencephalon
Made of crura cerebra, tectum, tegmentum, and cerebral peduncle
Forebrain
Comprised of the diencephalon and the telencephalon
Diencephalon
The anterior-most portion of the brainstem
Its most ventral part = the hypothalamus
Also includes the thalamus and the epithalamus
Hypothalamus
Subdivided into a number of discrete regions
Regulates most of the central and neuroendocrine functions in the body
Epithalamus
Includes the pineal gland
Thalamus
The relay and integration center of the brain
Telencephalon
Formed by the two cerebral hemispheres
Cranial nerves and types of innervations
Cranial nerves can be classified into groups based on 3 types of innervation:
1. Nerves responsible for special senses
2. Nerves that provide innervation to head muscles
3. Nerves that provide innervation to structures originating from the pharyngeal arch
Traditional classification of cranial nerves
Traditionally, cranial nerves have been grouped in a numerical order from anterior to posterior aka rostrocaudally based on their origin from the brain
There are 12 cranial nerves
Olfactory nerves (CN I)
Role: olfactory nerve fibers pierce through the cribriform plate of the ethmoid bone of the nasal cavity
Origin: the olfactory bulb of the brain
Optic nerve (CN II)
Role: vision
Origin: the diencephalon
Structure: connects the diencephalon with the eye retina → the optic tracts cross over at the optic chasm → the optic nerve exits via the optic foramen in the skull
Occulomotor nerve (CN III)
Structure; contains both somatic and autonomic fibers (visceral efferent → parasympathetic) → this nerve exits from the midbrain (both components) close to the midline
Role of its somatic component: provides motor innervation to some of the muscles of the eyeball → dorsal, medial, and ventral recti muscles → levator palpebrae superioris and the ventral oblique
Trochlear nerve (CN IV)
Role: innervates the dorsal oblique muscle of the eyeball
Origin: arises from the midbrain
Structure: one of the smallest of the 12 cranial nerves; starts @ the midbrain → innervates the eyeball’s dorsal oblique muscle → exits via the orbital fissure of the skull
Trigeminal nerve (CN V)
Role: provides motor innervation to muscles of mandibular (lower jaw) origin
Structure: the largest sensory nerve among cranial nerves; 3 divisions of the nerve: ophthalmic (pertaining to eye), maxillary (pertaining to upper jaw), and mandibular (pertaining to lower jaw)
Mandibular nerve exits via the oval foramen of skull
Ophthalmic nerve exits via the orbital fissure of the skull
Maxillary nerve exits via the round foramen of the skull
Abducent nerve (CN VI)
Role: innervates the lateral rectus and retractor bulbi muscles of the eyeball → draws the eyeball into the socket
Structure: starts from the caudal brainstem → exits the skull via the orbital fissure
Facial nerve (CN VII)
Role: its somatic component innervates muscles of facial expression
Structure; starts from the brain stem → exits the skull via the stylomastoid foramen. Also has a parasympathetic component
Vestibulocochlear nerve (CN VIII)
Role: responsible for the special senses related to vestibular (the ear’s location and movement perception functions) and cochlear (the ear’s auditory part) function
Structure: starts from the brain stem
Glossopharyngeal nerve (CN IX)
Role: provides sensory innervation tothe tongue’s mucosa and the pharyngeal regions; also provides some motor innervation to the pharyngeal region
Structure: originates @ the brain stem; has bothparasympathetic and somatic sensory and motor components
Vagus nerve (CN X)
Structure: contains visceral afferent, parasympathetic, and somatic efferent (motor) fibers
Role of the parasympathetic fibers: parasympathetic innervation to visceral organs in the thoracic and abdominal area
Role of the visceral afferent fibers: make up most the fibers in vagus nerves → provide afferent information from the viscera to the brain
Role of the small motor component: provides innervation to the laryngeal muscles
Accessory nerve (CN XI)
Structure: starts from the brain stem → divides into dorsal and ventral branches
Role of the dorsal branch = innervates muscles in the neck → brachiocephalicus, omotransversarius, trapezius
Role of the ventral branch = innervates sternocephalicus
Hypoglossal nerve (CN XII)
Role: provides motor innervation to muscles of the tongue
Structure: starts from the brain stem → exits the skull via hypoglossal canal
