Brain
Topics Covered
Introduction
Overview
Structure of a neuron
The synapse
The brain
Directional terms
Cerebrum
The cerebellum
The brainstem
Cranial meninges
Brain ventricles
Cerebrospinal fluid
Introduction
Subdivisions of the Nervous System
Two major anatomical subdivisions
• Central nervous system (CNS)
• Brain & spinal cord enclosed in bony coverings
• Peripheral nervous system (PNS)
• Nerve = bundle of nerve fibers in connective tissue
• Ganglion = swelling of cell bodies in a nerve
Structure of a Neuron
(link to figure 12.8- Parts of a Neuron)
• Cell body = perikaryon= soma
o
single,
central nucleus with large
nucleolus
• Dendrites - for receiving signals
• Axon - (nerve fiber) arising from axon hillock for rapid conduction
• Schwann cells – wrap around axons; contain myelin; Forms myelin sheath (increased speed)
o White matter (myelinated)
o Gray matter (unmyelinated)
Chemical Synapse Structure
(link to figure 12.27- The Synapse)
• Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have receptors
The Brain
Directional terms and landmarks
• Rostral (toward the forehead) - Caudal (toward the cord)
• Major parts of the brain - cerebrum, cerebellum, brainstem
o cerebrum is 83% of brain volume; cerebellum contains 50% of the neurons
o Brainstem – diencephalon, cerebral peduncles, midbrain, pons, medulla oblongata
Fore-, Mid-, and Hindbrain
• Forebrain
o Cerebrum
o Corpus callosum
o Diencephalon (Pineal gland, Thalamus, Hypothalamus, Pituitary gland, Mammillary bodies)
• Midbrain
o Cerebral peduncles
o Superior and Inferior colliculi
• Hindbrain
(link to figure 13.12- the brain stem)
o Pons
o Medulla oblongata
o Cerebellum
Cerebrum
(link to figure 13.6- the cerebrum)
• Longitudinal fissure separates 2 cerebral hemispheres.
o Gyri are the folds and sulci the grooves
o Surface layer of gray matter is called cortex; deeper masses of gray matter are called nuclei
• Bundles of axons (white matter) are called tracts;
• Cerebral cortex is 3mm layer of gray matter with extensive folds to increase surface area—divided into lobes
Functions of Cerebral Lobes
(link to figure 13.7- lobes of the cerebral cortex)
• Frontal contains voluntary motor functions and areas for planning, mood, smell and social judgment
• Parietal contains areas for sensory reception & integration of sensory information
• Occipital is visual center of brain
• Temporal contains areas for hearing, smell, learning, memory, emotional behavior
The cerebellum
(link to figure 13.13- the cerebellum)
• Connected to brainstem by cerebellar peduncles
• White matter (arbor vitae) visible in sagittal section
• Sits atop the 4th ventricle
The brainstem
Pons
•
Bulge in the brainstem, rostral to
the medulla
• Nuclei concerned with sleep, hearing, balance, taste, eye movements, facial expression, facial sensation, respiration, swallowing, bladder control & posture
Cranial meninges
Link to figure 13.17- meningeal layers of superior sagittal sinus
Brain ventricles
Link to figure 13.18- cerebrospinal fluid circulation
Cerebrospinal fluid
• Clear liquid fills ventricles and canals & bathes its external surface (in subarachnoid space)
• Goes into ventricles from choroid plexus
• Functions
o Buoyancy -- floats brain so it neutrally buoyant
o Protection -- cushions from hitting inside of skull
o Chemical stability -- rinses away wastes