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The nervous system is broadly divided into two regions
- Peripheral
nervous system – located outside bony structures
- Central
nervous system – located within skull and vertebral column
- There
are 7 main regions
- Spinal
cord (1)
- Brain
- Cerebrum
- Cerebral
hemispheres (2)
- Diencephalon
(3)
- Brainstem
- Medulla
(4)
- Pons
(5)
- Midbrain
(6)
- Cerebellum
(7)
We will start by looking at the gross neuroanatomy of the
central nervous system, starting with the brain.
Our brains weigh about 400 grams at birth.
The weight triples over the first 3 years of life.
This is not from the formation of new neurons, but instead from
myelination and the formation of new processes.
Growth weight then slows. Maximal
growth occurs by age 11, with an average brain size of 1400 grams.
Range is about 1100 to 1700 grams. In
general, the brains of men are larger than women, but women’s brains are
larger based on weight.
We will start with the Cerebrum and work our way caudally
There are two cerebral hemispheres
- Separated
by the longitudinal fissure
- Connected
by the corpus callosum
- Splenium
- Body
- Genu
- Rostrum
External structures on the surface of the cerebral
hemispheres: The brain surface is
folded. This functions to increase
the surface area of the cerebral hemispheres.
- Gyrus
(Gyri)
- Sulcus
(sulci)
- Fissure
The specific pattern of folding differs between people –
for example look at the pictures of human brains in the textbooks and the human
brains we will examine in lab.
.
There are several major sulci that are on the surface of
the cerebral hemispheres. Four of
these sulci, along with some other structures divide the hemisphere into lobes
- Central
sulcus – sulcus of Rolando
- Lateral
sulcus – fissure of Sylvius
- Parieto-occipital
sulcus
- Cingulate
sulcus
- Preoccipital
notch
Lobes of the Cerebral Cortex
Functions of the different lobes
Frontal Lobe
- Gyri
- On
lateral surface
- Superior
frontal gyrus
- Middle
frontal gyrus
- Inferior
frontal gyrus
- Orbital
part
- Triangular
part
- Opercular
- Precentral
gyrus
- On
inferior surface
- Orbital
gyri or orbitofrontal cortex
- Olfactory
sulcus – olfactory bulb and tract
- On
medial surface
- Continuation
of Superior frontal and precentral gyri
- Sulci
- Precentral
sulcus
- Superior
and inferior frontal sulci
- Functional
areas – 4 main functional areas
- Primary
motor cortex
- Most
of precentral gyrus on lateral and medial sides of cortex
- Many
of the cells of origin of descending motor pathways (upper motor
neurons)
- Involved
in the initiation of voluntary movements
- Premotor
and supplementary motor areas
- Rest
of precentral gyrus and areas of superior and middle frontal gyri
anterior to the precentral gyrus
- Also
has upper motor neurons
- Also
related to initiation of voluntary movements – more complex movements
that primary motor cortex
- Broca’s
area
- Opercular
and triangular parts of inferior frontal gyrus
- Production
of written and spoken language
- Prefrontal
cortex
- Rest
of frontal cortex
- Personality,
insight and foresight
Parietal lobe
Gyri
- On
lateral surface
- Postcentral
gyrus – posterior and parallel to central sulcus
- Superior
parietal lobules
- Inferior
parietal lobules
- Supramarginal
gyrus
- Angular
gyrus
- On
medial surface
- Continuation
of postcentral gyrus
- The
continuation of the postcentral and precentral gyri on the medial
surface of the brain are termed the paracentral lobule, which is partly
in the frontal lobe and partly in the parietal lobe.
- Precuneus
Sulci
- Postcentral
sulcus
- Intraparietal
sulcus
Function – three main functions
- Postcentral
gyrus and posterior paracentral lobule – primary somatosensory cortex –
initial cortical processing of sensory information: touch and proprioceptive
information
- Most
of the inferior parietal lobule on one side (usually left) and adjacent
parts of the temporal lobe are involved in comprehension and meaning of
language, both hearing and speaking
- Rest
of the parietal lobe: complex aspects of spatial orientation and perception
Temporal Lobe
Gyri
- On
lateral surface
- Superior,
middle and inferior temporal gyri
- On
superior surface
- Part
of superior temporal gyrus
- On
inferior surface
- Continuation
of inferior temporal gyrus
- Occipitotemporal
gyrus
Functions – 4 main functions
- Part
of superior temporal gyrus – primary auditory cortex
- Wernicke’s
area: part of posterior superior temporal gyrus on one side (same as areas
of parietal lobe, usually left). Important
for comprehension of language
- Most
of temporal lobe, particularly inferior surface, is involved in the higher
order processing of visual information
- Most
medial part is involved in complex actions of learning and memory.
The book actually considers this to be part of the limbic lobe
Occipital lobe
Gyri
- Lateral
occipital gyri
- On
medial surface
Sulcus
Functions – visual functions
- Primary
visual cortex
- Walls
of calcarine sulcus and adjacent cortex
- Visual
association cortex
- Remainder
of occipital cortex
- Higher
order processing of visual information
- Extends
somewhat into temporal cortex
Limbic lobe – on medial side of cerebral hemispheres
gyri
- Cingulate
gyrus
- Superior
to corpus callosum
- Parahippocampal
gyrus
- Continuation
of cingulate gyrus posterior to the splenium of the corpus callosum
- The
anterior end of the parahippocampal gyrus curves back on itself to form
the uncus
- Overall
travels adjacent to frontal, parietal, occipital and temporal lobes of
cortex
- Appear
to encircle the diencephalon – ‘limbus’ means border
Sulci
- Hippocampal
sulcus – at superior border of parahippocampal gyrus
- Deep
at this sulcus is the hippocampus (seahorse)
The limbic cortex and associated structures make up the
limbic system- which is important in emotions, drive-related behaviors and
memory.
DIENCEPHALON
Small region 2% of brain, but very important
4 main regions: the thalamus and 3 other regions named
after their relationship to the thalamus
Epithalamus
Hypothalamus
Subthalamic nucleus
The thalamus, hypothalamus, and epithalamus are midline
structures, and can be seen in a sagittal section of the brain.
Thalamus
- Egg-shaped
mass located on either side of the third ventricle
- Located
superiorly in the diencephalon
- Contains
many nuclei – groups of neuronal cell bodies
Functions
- Processing
station for sensory information – all sensory information, except for
olfaction, travels through the thalamus before it goes to sensory cortex
- Part
of two anatomical loops of the motor systems involving the basal ganglia and
cerebellum
- Cortex
à
Cerebellum à
Thalamus à
Cortex
- Cortex
à
Basal Ganglia à
Thalamus à
Cortex
- Also,
part of the limbic system. Limbic
projections go through the thalamus on their way to the cortex
Hypothalamus
Located below the thalamus
Separated from the thalamus by the hypothalamic Sulcus in
the wall of the third ventricle
Major visceral control center of the brain
Involved in limbic system function
Subthalamus
- Involved
with basal ganglia in motor functions
Epithalamus
- Pineal
gland (endocrine, not neural) and some small adjacent neural structures
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