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The Nervous System
Directions in the Nervous System
Dorsal or
Superior
Posterior
or Caudal
Anterior or
Rostral
Ventral or
Inferior
Medial
Lateral
Slice and Dice: Planes of View
Central and Peripheral Nervous Systems.
Divisions of the Nervous System
CNS - Division located within
the skull and spinal cord.
PNS – Division located outside
the skull and spine.
Afferent – Towards the CNS.
Efferent – Going away from the CNS.
PNS Divisions:
Somatic – interacts with external environment. Composed of afferent nerves
from skin, muscles, eyes, ears, etc., to the CNS and efferent nerves from the
CNS that carry signals to the skeletal muscles.
Autonomic – regulates internal environment. Afferent nerves carry signals
from internal organs to the CNS. Efferent nerves carry signals from the CNS to
internal organs. Sympathetic = autonomic motor nerves projecting from the
lumbar and thoracic regions of the spine. Parasympathetic = autonomic motor
nerves projecting from the brain and sacral region of the spine.
The Autonomic Nervous System
The Cranial Nerves
Peripheral Nerves Projecting Directly from the Brain.
Spinal Cord
Gray Matter = cell bodies,
unmyelinated axons. Dorsal and
Ventral Horns are gray matter.
White Matter = myelinated
axons
Spinal Nerves are attached to
spinal cord at 31 different levels
(62 spinal nerves).
Spinal Cord II
Dorsal root axons are
sensory unipolar neurons,
with their cell bodies
grouped just outside the
spinal cord forming the
dorsal root ganglion.
Synaptic terminals are in
dorsal horn.
Ventral Root Neurons are
motor (efferent) multipolar
neurons with their cell
bodies in the ventral horn.
The Ventricles and Cerebral Spinal
Fluid
Cerebral spinal fluid (CSF) is produced by the choroid plexus.
Choroid plexus – networks of small vessels that protrude into the
ventricle from the pia mater.
Dural Sinuses – Large blood filled cavities that absorb excess CSF.
The Blood-Brain Barrier
Impedes passage of many toxic substances into the brain.
Caused by the tightly packed cells of the cerebral blood vessels.
Astrocytes, a form of glial cell, further cover the walls of blood
vessels to help maintain this dense packing.
Differentially allows access of certain substances (I.e. hormones)
to particular parts of the brain.
Early Brain Development
Divisions of the Adult Brain
Myelencephalon and Metencephalon
Myelencephalon (also
called the medulla) is
composed largely of
fiber tracts. The
Reticular formation
(little net) plays a role in
arousal, attention, sleep
and various cardiac,
respiratory and
circulatory reflexes.
Metencephalon: 2 Division (1) Pons (ascending and descending
fiber tracks and part of reticular formation. (2) Cerebellum (little
brain) is a sensorimotor structure controlling fine motor
movements.
Mesencephalon
2 Divisions:
(1) Tectum or
“roof” which is
composed of two
bumps called
colliculi (little
hills). There is an
superior and an
inferior pair of
colliculi. Vision.
(2) Tegmentum, ventral to the tectum, contains the RAF, fiber tracts,
and the periaqueductal gray (pain and analgesia, especially opiates),
the substantia nigra (sensorimotor), and the red nucleus
(sensorimotor).
Diencephalon
Composed of the Thalamus and the Hypothalamus. The thalamus is the top of the
brainstem, and the two lobes are joined by the massa intermedia. In between the
lobes is the 3rd ventricle. Below lies the Hypothalamus, which exerts it’s effects by
releasing hormones from the pituitary gland. (Pituitary actually means “snot”).
Thalamus
Most Thalamic nuclei project to the cortex. Some are sensory relay
nuclei such as the lateral geniculate nucleus (visual), medial
geniculate nuclei (auditory) and ventral posterior nuclei
(somatosensory).
Hypothalamus
Below (hypo) the thalamus: Regulates release of hormones from pituitary gland.
On the ventral surface is the optic chiasm where the optic nerves from the eyes
come together. Most decussate or cross over to the other hemisphere of the brain
here, while others remain ipsilateral. The mammilary bodiesare also on the ventral
surface and involved in swallowing and olfaction.
Telencephalon: Major Fissures
Lobes of the brain
Lobes and Important Gyri
Layers of the Cortex
The Limbic System
Limbic = ring (of subcortical structures).
Regulation of motivated behaviors “the four F’s”
Fleeing; Fighting; Feeding; and Sexual Behavior
Basal Ganglia
Voluntary motor responses.
Note the amygdala is considered part of both
the limbic system and basal ganglia.
Types of Neurons
The Neuron
The Cell Membrane
The Neuron
Inside the Neuron
The Neuron
Myelination
Schwann
Oligodendrocyte
Astrocytes