Chapter 9Nervous system 9.14
9.14 Brain
Brain • Composed of 100 billion multipolar neurons • 4 major portions • Cerebrum – sensory, motor, and higher mental functions • Diencephalon – sensory info • Brainstem – regulates certain visceral activities • Cerebellum – coordinates voluntary muscular movement
Structure of the Cerebrum • Consists of the left and right cerebral hemispheres • Corpus callosum connects the 2 hemispherses • Ridges (gyri) separated by shallow grooves (sulci)
Structure of the Cerebrum • Fissures are deep grooves • Longitudinal fissure separates the left and right hemispheres • Transverse fissure separates the cerebrum from the cerebellum
Structure of the Cerebrum • 5 lobes • Frontal (anterior) • Parietal (superior) • Temporal (lateral) • Occipital (posterior) • Insula (deep within)
Structure of the Cerebrum • Outer layer (cerebral cortex) • Thin layer of gray matter • Contains nearly 75% of the neuron cell bodies in the nervous system • Inner mass • White matter makes up the bulk of the cerebrum • Communicate between the 2 hemispheres by way of the corpus callosum
Functions of the Cerebrum • Provides higher brain functions • Interprets sensory impulses • Initiates voluntary muscular movements • Stores info that comprises memory • Utilizes it to reason • Intelligence • Personality
Functions of the Cerebrum • Motor areas • In frontal lobes • Pyrimidal cells (upper motor neurons) connect to lower motor neurons whose axons leave the spinal cord and connect to skeletal muscle fibers • Most axons in these tracts cross over in the brain stem • Sensory areas • Interpret impulses that arrive from sensory receptors (from skin, eyes, ears, etc) • Also cross over in the brain stem or spinal cord
Functions of the Cerebrum • Association areas • Connects sensory, motor, and other association areas • Analyze and interpret sensory experiences, oversee memory, reasoning, verbalizing, judgment, and emotion • Higher intellectual processes (concentrating, planning, complex problem solving, and judging consequences of behavior)
Functions of the Cerebrum • Wernicke’s area (sensory speech area) • Receives input from visual and auditory cortex • Necessary for understanding written and spoken language • Broca’s area (motor speech area) • Generates the movement of muscles necessary for speech
Hemisphere Dominance • Both hemispheres participate in basic functions • Your dominant hemisphere controls the ability to use and understand language (mostly left) • Nondominanthemisphere specializes in nonverbal functions • Motor tasks that require orientation of the body in space • Understanding and interpreting musical patterns • Nonverbal visual experiences • Emotional and intuitive thinking
Ventricles and Cerebrospinal Fluid • Ventricles – interconnected cavities that contain cerebrospinal fluid • Continuous with the central canal of the spinal cord • Lateral, third, and fourth ventricle, and cerebral aqueduct • The choroid plexuses secrete cerebrospinal fluid into the ventricles
Ventricles and Cerebrospinal Fluid • Cerebrospinal fluid • Formed in the lateral ventricles and circulates to others • Completely surrounds the brain and spinal cord • Protects organs (absorbs) forces that may damage them • Maintains a stable ionic concentration • Provides a pathway to the blood for wastes
Diencephalon • Located between the cerebral hemispheres and above the midbrain • Surrounds the third ventricle and composed of gray matter • Includes the thalamus, hypothalamus, optic tracts, optic chiasma, infundibulum, posterior pituitary gland, mammillary bodies, and pineal gland
Diencephalon • Thalamus • Receives all sensory impulses (except those for smell) and channels them to the appropriate regions of the cortex for interpretation • Produces general awareness of certain sensations (pain, touch, and temperature) • Hypothalamus • Maintains homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine systems
Diencephalon • Hypothalamus regulates • Heart rate and arterial blood pressure • Body temperature • Water and electrolyte balance • Control of hunger and body weight • Control of movements and glandular secretions of the stomach and intestines • Production of neurosecretory substances that stimulate the pituitary gland to secrete hormones • Sleep and wakefulness
Diencephalon • Limbic system • Controls emotional experience and expression • Can modify the way a person acts by producing feelings such as fear, anger, pleasure, and sorrow • Recognizes a persons physical or psychological condition and causes pleasant or unpleasant feelings to guide a person into behavior that is likely to increase the chance of survival
Brainstem • Brainstem – a bundle of nervous tissue that connects the cerebrum to the spinal cord • Includes the midbrain, pons, and medulla oblongata
Brainstem • Midbrain • contains the corticospinal tracts (main motor pathways between the cerebrum and the lower parts of the nervous system • Has reflex centers that orient the eyes and head in response to visual and auditory stimulation
Brainstem • Pons • Dorsal portion relays impulses to and from the medulla oblongata and the cerebrum • Ventral portion transmits impulses from the cerebrum to centers within the cerebellum
Brainstem • Medulla Oblongata • Cardiac center – alters heart rate • Vasomotor center – stimulate blood vessels to contract, raising blood pressure or dilates blood vessels, causing a drop in blood pressure • Respiratory center – adjusts the rate and depth of breathing and acts with the pons to maintain basic rhythmic breathing • Also associated with reflexes such as coughing, sneezing, swallowing, and vomiting
Brainstem • Reticular formation • Complex network of nerve fibers scattered throughout the medulla oblongata, pons, and midbrain • Sensory impulses activate the cerebral cortex into a state of wakefulness • Without arousal, the cortex remains unaware of stimulation • Decreased activity results in sleep
Cerebellum • Cerebellum – primarily made of white matter with a thin layer of gray matter (cerebellar cortex) on its surface • Has 3 pairs of nerve tracts called cerebellar peduncles • Inferior peduncles – brings sensory info concerning the position of the limbs, joints, and other body parts • Middle peduncles – transmits signals from the cerebral cortex to the cerebellum concerning the desired behavior of these parts • Superior peduncle – incorporates correcting impulses with motor impulses to move body parts in a desired way • Reflex center for integrating sensory info concerning the position of body parts and coordinating complex skeletal muscle movement
