L3 Anatomy of the Nervous System
1. General Layout of the Nervous - The Nervous System is divided between the Central Nervous
System System and the Peripheral Nervous System
- CNS is composed of the brain and spinal cord and consists of 12
Central nervous System pairs of cranial nerves with sensory or motor functions
Peripheral Nervous System o Ex. If one of the optic nerves are damaged, you can lose
sight in that eye.
o If there is a lesion in the visual cortex, you can only see
in the central region of the visual field.
- PNS is comprised of somatic and autonomic nervous systems and
have nerves that project from the spinal cord
- The Somatic Nervous system (SNS) is the part of the PNS that
Afferent nerves interacts with the external environment and is composed of
afferent nerves, which carry sensory signals from the skin,
skeletal muscles…etc to the CNS
Efferent Nerves - Efferent nerves carry motor signals from CNS skeletal
** think efferent = exit muscles.
- Autonomic Nervous System (ANS) is the part of the peripheral
Autonomic Nervous system nervous system that regulates the body’s internal environment.
Sympathetic nerves - Consists of sympathetic nerves, which are autonomic motor
Parasympathetic nerves nerves that project in the lumbar(back) and thoracic(chest) regions
- Parasympathetic nerves which project from brain and sacral
(lower back) of the spinal cord.
- Sympathetic neurons synapse onto second-stage neurons away
The Meninges from target but parasympathetic synapse on close distance.
- Type of deficit can tell us a lot about where in the brain the
- The brain and spinal cord are protected by the skull and vertebrae
Dura mater and 3 membranes/ meninges
Arachnoid mater 1. Dura mater ( tough mother) outer layer
Pia mater 2. Arachnoid mater (spidery mother)
- Beneath is the subarachnoid space, which has many large blood
vessels and cerebrospinal fluid.
The Ventricles and CSF 3. Pia mater ( gentle mother)
- Adheres to the surface of the CNS.
- Choroid plexuses, capillary networks that protrude into ventricles
manufactures the cerebrinospial fluid CSF
- CSF circulates through:
1. Ventricular system – cerebral ventricles are 4 large internal
chambers of the brain.
2. Central canal of spinal cord
3. Subarachnoid space
4. Absorbed through large channels/blood-filled spaces called
sinuses in the dura mater
5. Enters the jugular veins of the neck.
- The purpose of the CSF is to support and cushion the brain.
- If the flow of the CSF is blocked, maybe through a tumor,
Hydrocephalus hydrocephalus / too much fluid can increase intercerebral
pressure and brain damage can occur
- An operation in which a hole is drilled through the skull and a
shunt tube is inserted onto the ventricle beneath the skin, with a
pressure relief valve in the abdominal cavity, allows the CSF to
pass into the abdomen to be reabsorbed into the blood supply.
2. Neuroanatomical techniques 1. Golgi stain permitted individual neurons to be studied for the
first time if interested in seeing shape of neurons.
2. Nissl stain highlights cell bodies of all neurons, allowed
estimation of cell density in tissue and viewing structure 3. Electron microscopy allows visualization of neuronal
ultrastructure – extremely detailed
4. Myelin Stain: highlights myelinated pathways; less useful
for studying individual axons
5. Tract tracing techniques: highlight individual axons; may
be retrograde (trace back from terminal fields) or anterograde
(trace from soma terminal fields) by injecting chemicals
and tracing their paths.
3. Orientation and Direction in the - Directions in the nervous system are normally described relative
Vertebrate Nervous System to the neuraxis, an imaginary line drawn though the spinal cord
Neuraxis up to the front of the forebrain.
**This can be a little confusing because some of the terms differ depending on
whether you’re an animal with a linear neuraxis (alligator) or upright (human)
Anterior - Anterior means toward the nose or front
Posterior - Posterior: toward the tail or back
Dorsal - Dorsal is toward the surface of the back or top of the head (ex.
Ventral Dorsal fin)
- Ventral is the surface of the chest or bottom of the head
- Superior and Inferior are also used to refer to the top and bottom
of the primate head.
Medial - Medial is toward the midline of the body
Lateral - Lateral is outside or away from the midline.
Slicing Planes 1. Horizontal: a
Horizontal slice parallel to the ground
Transverse/cross-section/frontal 2. Transverse /
cross-section/frontal : A slice you
would get if slicing a loaf of bread
Sagittal or salami / vertical.
** Because of our upright posture,
cross sections of the spinal cord
are parallel to the ground and right
3. Sagittal: A
midsagittal section that separates the left and right halves of
Describing Brain Damage - Ipsilateral (same side of body) or contralateral (on opposite
o Ex. Stroke to one side of the brain can cause motor
problems on the opposite side of the body or
The Crossed Brain contralateral side.
- Each of its symmetrical halves responds to sensory stimulation
from the opposite or contralateral side of the body as well as
controlling the muscles on the opposite side.
- Since nearly all fibers of motor and somatosensory systems cross,
numerous crossings or decussations of sensory and motor fibres
are found along the center of the nervous system.
4. Blood Supply to the Brain - The brain receives ~20% of blood flow from the heart because it
can’t store fuel or temporarily extract energy without oxygen
- Therefore a consistent blood supply is essential
Major Arteries to the Brain
- Two systems of arteries supply blood to the brain:
Carotid 1. Carotid arteries
- Arise in the neck and co externally (face/scalp) and internally to
the anterior 3/5 of the cerebrum
Vertebral 2. Vertebral arteries - Go from the posterior 2/5 of the cerebrum, cerebellum and
Circle of Willis - The carotid and vertebasilar arteries form a circle of
communicating arteries called the Circle of Willis
- The anterior, middle and posterial cerebral all come from this
Circle gives rise to branches that supply the cortex and deeper
structures (basal ganglia, thalamus, and internal capsule) with
- Having 2 major sources of blood supply improves the chances of
any region of the brain to receive blood if a major artery is
Blood Brain Barrier
- Exists between the blood and the fluid that surrounds the cells of
- It is selectively permeable. Capillaries in the brain don’t have caps
in them and therefore many substances can’t leave the blood.
- Since messages are transmitted within the brain and if
composition of the intracellular and extracellular fluids of neurons
is changed even slightly, the transmission of information would be
- This barrier isn’t uniform
o Ex. Medulla oblongata – area postrema region that
controls vomiting has a thin blood-brain barrier so it can
detect the presence of toxic substances in the blood.
- The blood-brain barrier doesn’t impede the passage of all large
molecules, some large molecules that are critical for normal brain
function (e.g. glucose) are actively transported through cerebral
blood vessel walls.
T: pg 51-74
1. Neurons - Neurons are cells that are specialized for the reception,
conduction and transmission of electrochemical signals.
External Anatomy of Neurons
1. Cell membrane: the semipermeable membrane that encloses
2. Dendrites: the short processes emanating from the cell body,
which receive most of the synaptic contacts from other
3. Axon hillock: the cone shaped region at the junction
between the axon and the cell body.
4. Cell body: the metabolic center of the neuron, also called the
5. Axon: the long narrow process that projects from the cell
6. Myelin: the fatty insulation around many axons
7. Nodes of Ranvier: Gaps between sections of myelin
8. Buttons: the buttonlike endings of the axon branches, which
release chemicals into synapses