UNIT 5: Nervous System – part 4 THE HUMAN BRAIN

Protective Structures The brain and spinal cord are delicate and vital organs and are protected by two coverings 1. Outer bone coverings 2. Inner membranes called the “meninges” Between the bone & the meninges: protection = cerebrospinal fluid –Cushions & nourishes the brain & spinal cord

Meninges –Consists of 3 layers Dura mater – “Tough Mother” –Outer layer –Made of a thick fibrous tissue –Also has extensions which separate parts of the brain Arachnoid mater –Middle layer –Delicate, cobweb like-layer Pia mater –Innermost layer –Transparent and adheres to blood vessels on the outer surface of the brain and spinal cord

Meningitis An infection or inflammation of the meninges is called meningitis –Usually caused by bacteria but could also be viral or the result of a tumor –Generally affects the arachnoid mater or the pia mater –Symptoms include fever, severe headaches, neck stiffness, and pain –Meningitis may range from a mild condition to a fatal illness

Brain Facts The brain is one of the largest organs in the adult human body –It weighs about 3 lbs. –Also contains about 100 billion neurons and 900 billion glial cells –The brain grow rapidly through the first 9 years, attains full size by the 18 th year

Parts of the Brain: The brain has 4 main regions: 1)CEREBRUM 2)CEREBELLUM 3)BRAIN STEM 4)DIENCEPHALON

1) CEREBRUM:  Divided into hemispheres (R and L)  Each hemisphere divided into lobes (frontal, parietal, temporal, occipital)  Each hemisphere has a highly folded outer covering of gray matter = CEREBRAL CORTEX  Hemispheres are connected by white matter called CORPUS CALLOSUM

CEREBRUM – functions!  Where memories are stored  Interprets sensory impulses arriving from sense organs  Centers for motor coordination; send motor impulses to muscles  Where conscious decisions are made  Intelligence and personality stem from cerebral activity

 2 functional cortical areas: 1) Motor Cortex: sends commands to skeletal muscles

2) Somatosensory Cortex: *Receives and integrates signals from touch, pain, pressure, and temperature receptors; *Divided into specific areas so that we can associate specific stimuli with specific parts of the body.

3) Association Areas: Neither primarily motor nor sensory –they connect with one another and with other brain areas Analyze & interpret sensory experiences Oversee memory, reasoning, verbalizing, judgment, & emotion –Ex: association areas of the frontal lobe control many higher intellectual processes vs. assoc. areas in occipital lobes deal with visual interpretation

Language Language functions consist of the ability to speak and write words, and the ability to understand spoken and written words. –Broca’s area is a large speech center located in the frontal lobe Damage to Broca’s area would cause a person to be unable to articulate words, but still make vocal sounds and understand written and spoken language –Wernicke’s area is located posteriorly in the temporal lobe This area is responsible for understanding written and spoken language

Specialization of Cerebral Hemispheres The right and left hemispheres of the cerebrum specialize in different functions –The left hemisphere: language functions, and dominates hand movements (especially skilled gestures and movements) Most of the population uses their right hands –The right hemisphere: perception of certain auditory stimuli, tactual perception, and in perceiving and visualizing spatial relationships –Despite specializations in each hemisphere, both hemispheres communicate with each other through the corpus collosum

2) CEREBELLUM: coordination of movement; balance; hand-eye coordination

3) BRAINSTEM:  superior end of spinal cord;  3 parts that function in: -HOMEOSTASIS -Movement coordination -Conduction of info. to higher brain centers:

1) Medulla oblongata: controls involuntary reflexes like breathing, heart and blood vessel activity, swallowing, vomiting, digestion

2) Pons: regulates breathing centers in the medulla oblongata

3) Midbrain: receives and sends sensory information that coordinates eye movements/head movements to respond to stimuli

4) DIENCEPHALON (Between Brain) : Located between the cerebral hemispheres and above the midbrain. Includes the: –thalamus –hypothalamus –optic tracts & optic chiasma –posterior pituitary gland –pineal gland

THALAMUS: relay center that sorts out & transmits sensory info. to and from cerebrum

HYPOTHALAMUS:  Important regulator of HOMEOSTASIS  Contains body’s thermostat (regulates temperature)  Includes centers for regulating hunger & thirst  Plays role in sexual response and mating behavior  Fight-or-flight response, pleasure, daily biorhythms

Pineal Gland (Body) Located below the hypothalamus and named pineal gland because its structure resembles a small pinecone –Functions of the pineal gland are not well understood but it is thought to be involved in regulating the body’s biological clock Produces the hormone melatonin, which is thought to synchronize various body functions with each other and external stimuli

Optic Chiasma Region where the right and left optic nerves cross each other before entering the brain