Central Nervous System

The Brain

• 2 hemispheres and 4 major portions

• one of the largest organs (3 lbs)

• contains approximately 100 billion neurons

• made up of gray matter (cell bodies) and white matter (axons with myelin)

Brain Stem: medulla oblongata, pons, and midbrain

• Medulla oblongata – Cardiac center- regulates heartbeat– respiratory center – rate, rhythm, and depth

of breathing– vasomotor center – regulates dilation of

blood vessels– other: swallowing, coughing, sneezing,

hiccupping, vomiting

Brain Stem: medulla oblongata, pons, and midbrain

• Pons : “bridge” – connects medulla oblongata to midbrain– transmits impulses from the cerebrum to

the cerebellum

• Midbrain – controls reflexive movements of head and

eyes in response to visual stimuli – controls reflexive movements of head and

trunk in response to auditory stimuli

Diencephalon

• Thalamus– central relay station for sensory impulses

(except smell)– interpretation center for pain, temperature,

light touch, pressure

Diencephalon• Hypothalamus

– body temperature– water balance– control of hunger and body weight– control of movements and glandular

secretions of the stomach and intestines– production of hormones that stimulate the

pituitary gland to secrete other hormones– sleep and wakefulness– limbic system (emotional (experiences &

expression), memory)

Cerebellum

• coordinates but does not initiate voluntary motor action

• coordination• maintains posture/balance• damage to the cerebellum will likely result in

tremors, inaccurate movement of voluntary muscles, loss of muscle tone, loss of equilibrium

• Pons important bc relays info between cerebrum (Mvnt) and cerebellum (coordination)

Cerebrum• many raised folds called gyri• the deep grooves are called sulci• consists of 2 hemispheres connected by nerve fibers

called the corpus callosum• has four lobes: frontal, parietal, temporal, occipital• provides higher order mental functions• interprets sensory impulses and initiates voluntary

muscular movements• stores memory and uses it for reason• intelligence and personality stem from cerebral activity

Lobes of the Cerebrum• Frontal

– primary motor area for upper and lower limbs– Broca’s area – (SPEECH) coordinates tongue,

mouth, and larynx for speech– movement of the eyes and eyelids– higher intellectual processes like problem

solving.• Parietal

– Receives and sends out sensory input (Senses); temperature, touch, pressure, pain in the skin

– understanding speech and using words to express feelings and thought

Lobes of the Cerebrum

• Temporal– hearing– interpreting sensory experiences, visual

scenes, music and patterns• Occipital

– vision– combining visual experiences with other

sensory experiences; recognition

Meninges

• found between bone and soft tissue of the nervous system; cover and protect brain and spinal cord – dura mater “tough mother”- outer most

covering– arachnoid mater “spider” - middle layer

• Well Vascularized – therefore main site of blood brain barrier.

– pia mater “ delicate”- inner layer

Blood Brain Barrier• BLOOD-BRAIN BARRIER• capillary walls in brain contain more densely packed cells

(called astrocytes) and have a continuous basement membrane

• This protects the brain by keeping toxins out and protecting brain from a direct rise in temperature (fever).

• Some substances permeable through barrier:– Water - Carbon dioxide - Glucose– Insulin - Alcohol - Heroin -

Nicotine• Some substances impermeable to the barrier:

– Hydrogen ions - Proteins - Antibiotics

• Other characteristics of blood brain barrier:• Trauma can destroy it and lead to brain injury• Keeps out many useful drugs; researchers are developing

ways to attach drugs to molecules that can cross the barrier

Spinal Cord

• column of nerve tissue that starts in the medulla oblongata and runs down the vertebral column

• consists of 31 segments; each associated with a pair of spinal nerves

• contains a core of gray matter that roughly resembles a butterfly with its wings spread or a flattened H; surrounded by white matter

• conveys sensory impulses from PNS to the brain and conducts motor impulses from brain to PNS