Unit 6: Nervous System: Brain

Central Nervous System

Divisions of the Brain

• Brainstem - Medulla Oblongata, Pons, and Midbrain

• Cerebellum

• Diencephalon - Hypothalamus, Thalamus, and Pineal Gland

• Cerebrum

Coverings and Fluid Spaces

Brainstem

Consists of three parts of brain, named in ascending order

• Medulla oblongata

• Pons

• Midbrain

Structure

• White matter with bits of gray matter scattered through it

Functions

• All three parts of brainstem conduct impulses to the higher parts of the brain

Midbrain

• Located at the top of the brainstem right below the cerebellum and above the pons

• All neuronal transmissions pass through the midbrain

• Helps to manage auditory and visual sensory information relays and plays a role in attention and alertness 

• Motor reflexes specific to visual and auditory stimuli via cranial nerves

Pons

• Located in the middle of the brainstem

• Relays information about motor function, eye movement, sensation, hearing and taste

• Plays a role in the autonomic nervous system 

• 4 cranial nerves exit from the Pons

• Involved in the reticular activating system related to sleep wake, attention and pain

Medulla Oblongata

• Lies just above the foramen magnum (the opening through which the spinal cord passes)

• Assists in communication between the CNS and PNS

• 4 cranial nerves exit here

• Controls autonomic nervous system functions such as

• ➢ Respiration

• ➢ Digestion

• ➢ Heart rate

• ➢ Blood vessels (BP regulation)

• ➢ Swallowing

• ➢ Sneezing

Reticular Formation

• Decides what sensory information will be sent to the cerebrum

• Acts as a “filter” for conscious awareness of sensory information

Cerebellum

Structure

• Second Largest part of the human brain

• Gray matter outer layer is thin but highly folded, forming a large surface area for processing information

• Arbor vitae

Function

• Helps control muscle contractions to produce coordinated movements for maintaining balance, moving smoothly, and sustaining normal postures

• Variety of additional coordinating effects, assisting the cerebrum and other regions of the brain

Arbor vitae

Internal, treelike network of white matter tracts

Diencephalon

• Hypothalamus

• Thalamus

• Pineal Gland

Hypothalamus

• Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter

• Acts as the major center for controlling the ANS; therefore, it helps control the functioning of most internal organs

• Controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands

• Contains centers for controlling body temperature, appetite, wakefulness, and pleasure

Thalamus

• Dumbbell-shaped mass of gray matter extending toward each cerebral hemisphere

• Relays sensory impulses to cerebral cortex sensory areas

• In some way produces the emotions of pleasantness or unpleasantness associated with sensations

Pineal gland

• Small body resembling a pine nut behind the thalamus

• Adjusts output of “time-keeping hormone” melatonin in response to changing levels of external light (sunlight and moonlight)

Cerebrum

Largest part of the human brain

Outer layers of gray matter are the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons

Interior composed mainly of white matter

• Tracts

• Basal nuclei

Functions

• Mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements

Tracts

Nerve fibers arranged in bundles

Basal nuclei

Islands of gray matter regulate automatic movements and posture

Spinal Cord

Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core; bundles of axons called tracts

Interior composed of gray matter made up mainly of neuron dendrites and cell bodies

Tracts provide two-way conduction paths: Ascending and descending

Functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain

Coverings

Cranial Bones and Vertebrae

Cerebral and spinal meninges

• Dura mater

• Pia mater

• Arachnoid mater

Fluid Spaces

• Subarachnoid spaces of meninges

• Central canal inside cord

• Ventricles in brain

Cerebrospinal Fluid (CSF)

Fluid that fills the subarachnoid spaces between the pia mater and arachnoid in the brain and spinal cord.

Cranial nerves

Twelve pairs: Attached to undersurface of the brain

Connect brain with the neck and structures in the thorax and abdomen

Spinal nerves

Thirty -one pairs: Contain dendrites of sensory neurons and axons of motor neurons

Conduct impulses necessary for sensations and voluntary movements

Dermatome

Dermatome

Skin surface area supplied by a single cranial or spinal nerve