Introduction to the Nervous System Flashcards
What Do Nerves Do?
Sensory Functions: Enable us to perceive internal and external environments.
Special Senses: Vision, hearing, taste, smell, and balance
Motor Functions: Facilitate appropriate responses to stimuli.
- Voluntary: Skeletal muscle movement (locomotion)
-
Involuntary: Smooth muscle, gland, and cardiac muscle actions
Reflex Functions: Automatic, rapid responses to stimuli.
Anatomical Subdivisions
Central Nervous System
Peripheral Nervous System
Describe the CNS
Brain
Spinal Cord
Central controller
Describe the PNS
All other nerve tissue not within the CNS
Spinal nerves
-connect with spinal cord
Cranial nerves
-connect with brain
Autonomic nerves
-organs, smooth muscle, glands
-visceral afferents
-sympathetic nerves
-parasympathetic nerves
Wiring
Describe The Neuron
Basic unit of nervous system
Collection of nerve cell bodies:
in CNS = Nucleus
in PNS = Ganglion
Describe Nerves
Bundles of Axons (nerve fibres): Wrapped in connective tissue, traveling to/from same regions or structures.
Can branch off as smaller bundles
Named Nerves: Larger nerves serving the body wall, cavities, and organs
What is in a Nerve?
A single nerve fiber (axon) only conducts action potentials for ONE of six modalities:
1. Somatic sensory function
2. Somatic motor function
3. Special sensory function
4. Visceral afferent function
5. Sympathetic function
6. Parasympathetic function
Motor Vs Sensory
Motor (efferent):
Action potential towards body wall, body cavity or organ
Sensory (afferent):
Action potential towards brain
Describe The Brain
outermost layer of the cerebral hemispheres cortex
consists of gyri and sulci
4 lobes of each cerebral hemisphere
named according to cranial bone they lie deep to
What is the Cranial Nerves
12 pairs - need to know name, number (Roman numerals), modality and function(s), where they connect to CNS, route through and exit from cranium
CN I
-olfactory nerve
-sensory (special)
CN II
optic nerve
sensory (special)
CN III
oculomotor nerve
motor (somatic & parasym.)
CN IV
trochlear nerve
motor
CN V
trigeminal nerve
both
CN VI
abducent nerve
motor
CN VII
facial nerve
both (spec.sensory, somatic motor & parasym.)
CN VIII
vestibulocochlear nerve
sensory (special)
CN IX
glossopharyngeal nerve
both (spec.sensory, somatic motor & parasym.)
CN X
vagus nerve
both (somatic sensory, somatic motor & parasym.)
CN XI
spinal accessory nerve
motor
CN XII
hypoglossal nerve
motor
Where Cranial Fossae Foraminae for CNs to enter/exit cranial cavity:
Course of a Cranial Nerve
The Spinal Cord
Passes through foramen magnum
Protected by vertebral canal
Has 4 segments:
cervical
thoracic
lumbar
sacral/coccygeal
Has 2 enlargements
cervical
lumbosacral
Connects bilaterally with spinal nerves
8 cervical - C1-C8
12 thoracic - T1-T12
5 lumbar - L1-L5
5 sacral - S1-S5
1 coccygeal - Co
spinal cord ends at L1/L2 IV disc level
conus medullaris
Adult vertebral column is longer than the adult spinal cord
lumbar and sacral spinal nerve roots have to descend in the vertebral canal to their respective intervertebral foraminae
cauda equina (horse’s tail)
How are Spinal nerves named?
- according to the vertebrae above it
- except in the cervical region, where
they are named according to the
vertebrae below it - C8 spinal nerve exits between C7 and T1
vertebrae
Vertebral Column
33 vertebrae in total
7 cervical
12 thoracic
5 lumbar
5 sacral
fused to form 1 sacrum
4 coccygeal
fused to form 1 coccyx
Rules of spinal nerve anatomy:
- spinal nerves supply the soma (body wall)
- located only within the intervertebral foramina
- from the intervertebral foramina they connect with
- structures of the soma via rami
- the spinal cord via roots and rootlets
Anatomy of Spinal Nerves
Spinal Nerves and Body Segments
each pair of spinal nerves supplies one ‘strip’ of the soma
posterior rami
-supply small posterior strip
anterior rami
-supply the remainder of the posterior part, the lateral and the anterior parts of the strips
-supply all of the limbs
What is a Dermatomes
area (strip) of skin supplied by both the anterior and posterior rami of a spinal nerve
T4 dermatome – nipple
T10 dermatome – umbilicus
List Nerve Plexuses
Cervical plexus
C1-C4 anterior rami
Posterior scalp, neck wall and diaphragm
Brachial plexus
C5-T1 anterior rami
Upper limb
Lumbar plexus
L1-L4 anterior rami
Lower limb
Sacral plexus
L5-S4 anterior rami
Lower limb, gluteal region and perineum
Functional Subdivisions - Somatic nervous system
Soma includes:
-head and neck walls
-chest walls
-back
-the diaphragm
-abdominal wall
-pelvic wall
-limbs
Structures:
-skin
-fascia
-skeletal muscle
-skeleton
-internal lining of body cavities
Somatic Sensation- Sensations felt by body wall
sensed by mechanoreceptors:
-coarse touch
-fine touch
-vibration
-proprioception
sensed by thermoreceptors:
-temperature
sensed by nociceptors:
-pain
Describe Somatic Sensation
- Somatic sensory mechanoreceptors in the L2 dermatome are stimulated
- Action potentials (APs) travel via axons in the L2 anterior ramus
- These axons pass through the lumbar plexus to the L2 spinal nerve
- APs continue through the dorsal (posterior) root ganglion, dorsal roots, and rootlets
- APs reach the posterior horn of the L2 spinal cord segment
- APs cross the midline and ascend towards the brain
Describe Motor Innervation
Somatic motor axons cross in the brainstem and descend to the anterior horn.
APs travel through anterior rootlets, roots, and spinal nerves.
APs continue via lumbar plexus nerves to synapse on lower limb skeletal muscles.
Skeletal muscles contract, moving the lower limb.
Spinal Reflexes
-reflex is extremely rapid
-misses out pathway to brain
-involuntary response
Functional Subdivisions - Autonomic nervous system
Includes
Viscera e.g. heart, lungs, intestines, kidneys
glands (mucous, sweat, salivary etc.)
smooth & cardiac muscle
external lining of organs
Locations
internal organs in body cavities
chest cavity, pelvic cavity, abdominal cavity
body wall organs
sweat glands, arrector smooth muscles, arterioles
Describe the Autonomic Nervous System
Auto = self , nomos = law
Internal environment:
-Sensory neurones
-Sensations from organs to CNS
-Motor Neurones
Role of Sensory neurones in ANS
sense the internal environment (organs)
organs sensory nerves are called ‘visceral afferent’
Role of Sensations from organs to CNS in ANS
-Touch
-Temperature
-Pain
-Ischaemic
-Colicky
Described as:
– dull, achy, nauseating
- poorly localised
Role of Motor Neurones
in ANS
-respond to changes in internal environment
dual motor control
-Many internal organs have both a sympathetic & parasympathetic nerve supply
-Both motor controls
-‘Accelerator’ or ‘brake’
3 Things Sympathetic Division of ANS supplies
- all internal organs
- body wall organs
- arterioles
How do the following structures respond during ‘Flight or fight’
pupils, heart, lungs. GI tract, Liver, Adrenal Glands, Arterioles, Skin
Pupils - dilate
Heart - rate increases
Lungs - bronchioles dilate
GI tract - motility is reduced
Liver - glucose released into the blood
Adrenal glands - adrenaline/noradrenaline released
Arterioles - dilate or constrict- skin feels cold & looks pale
Skin - hair stands on end & sweat produced
Describe Sympathetic Outflow
Descends the spinal cord and exits with T1-L2 spinal nerves.
Travels to sympathetic chains along the vertebral column.
Distributes via spinal nerves, anterior/posterior rami, to body wall structures.
Follows arteries to supply head, neck, and skin.
Travels via splanchnic nerves to reach organs.
Which segments of the spinal cord have lateral horns and why?
T1- L2
for cell bodies of the next sympathetic neurones in the chain
Parasympathetic Division of ANS
Often supplies same internal organs as sympathetic division
Does not supply body wall organs or arterioles
Rest & Digest
-Returns to homeostasis
-Compliments / Opposes the sympathetic system
How do the following structures respond during ‘Rest and Digest’
pupils, heart, lungs, GI tract, liver, bladder
Pupils - constrict
Heart - rate decreases
Lungs - bronchioles constrict
GI tract - motility is increased
Liver - glucose synthesis
Bladder – sphincter relaxes
Describe Parasympathetic Outflow
- Parasympathetic axons exit via cranial nerves III, VII, IX, X, and sacral spinal nerves.
- Target internal organs, not the body wall.
- Cranial ganglia supply the lacrimal and salivary glands.
- Vagus nerve innervates neck, chest, and mid-gut organs.
- Sacral nerves carry axons to the hindgut, pelvis, and perineum
Modalities – Neuron Types
