Nervous System Anatomy Chapter 11

Meninges Meninges are membranes that cover and protect the brain and spinal cord There are three types of meninges: dura mater arachnoid mater pia mater  Cerebrospinal fluid occupies the space between the arachnoid and pia maters. This space is known as the subarachnoid space.

Spinal Cord The spinal cord is a nerve column that extends from the brain into the vertebral canal. It terminates at the level between the first and second lumbar vertebrae. The spinal cord is composed of 31 segments, each that have a pair of spinal nerves branching off from it. A CERVICAL enlargement occurs at the top of the spinal cord and a LUMBAR enlargement occurs at the bottom of the spinal cord.

Spinal Cord, cont. Two deep grooves divide the spinal cord into right and left halves. These grooves are known as: posterior median sulcus and anterior median fissure. The spinal cord has a central core made of GRAY matter, which is in turn, surrounded by WHITE matter. The function of the spinal cord is to provide a two-way communication system between the brain and structures outside the nervous system. This is achieved by ascending and descending tracts. An ascending tract carries SENSORY impulses to the brain; while descending tracts carry MOTOR impulses to muscles and glands.

Reflex Arcs A reflex arc is the behavioral unit of the nervous system and usually contains a sensory neuron, a reflex center composed of interneurons, and a motor neuron. REFLEXES are automatic, subconscious responses to change and they help maintain homeostasis.  Withdrawal reflexes are protective actions that usually occur when a person unexpectedly touches something painful.

Brain The brain is the largest and most complex part of the nervous system It contains nerve centers that are associated with sensations It issues motor commands and carries on higher mental functions

Brain Development The brain develops from a neural tube with three cavities—the FOREBRAIN, the MIDBRAIN, and the HINDBRAIN The cavities are known as ventricles and the walls give rise to structural and functional regions Ventricles are filled with cerebrospinal fluid CHOROID PLEXUSES in the walls of the ventricles secrete cerebrospinal fluid. The fluid’s composition is regulated by ependymal neuroglial cells Cerebrospinal fluid circulates through the ventricles and is REABSORBED into the blood of the dural sinuses

Parts of the Brain 1. Cerebrum: The cerebrum consists of two cerebral hemispheres connected by the CORPUS CALLOSUM SULCI divide each hemisphere into LOBES The cerebral cortex is a thin layer of gray matter (2-5mm) that makes up the outermost portion of the cerebrum. Nearly 75% of all neural cell bodies are found in the cerebral cortex The lobes that make up the cerebrum are: a. FRONTAL LOBE b. PARIETAL LOBE c. TEMPORAL LOBE d. OCCIPITAL LOBE e. INSULA

Functions of Cerebrum The cerebrum is concerned with higher brain functions, such as thought, reasoning, interpretation of sensory impulses, control of voluntary muscles, and memory storage The cerebral cortex has sensory, motor, and association areas. Primary motor regions lie in the frontal lobes Primary sensory regions lie in the parietal lobes, though some specialized sensory are found in the temporal and occipital lobes, as well Association areas analyze and interpret sensory impulses and provide memory, reasoning, verbalizing, judgment, and emotions One cerebral hemisphere usually dominates for certain intellectual functions. Short-term memory is thought to be electrical. Long-term memory is thought to be encoded in patterns of synaptic connection.

Functions of the Cerebral Lobes Frontal Lobe: controls voluntary movement Higher intellectual processes like problem solving and judging behavior Parietal Lobe: Sensation center for touch, pain, pressure, and temperature Understanding speech and using words to express thought and feeling Temporal Lobe: Sensation center for hearing Interpret senses and remember visual scenes, music, and patterns Occipital Lobe: Sensation center for vision Combine visual images with sensory experience Insula: Integrate autonomic information

Parts of the Brain, cont. 2. Diencephalon The diencephalon contains the THALAMUS and the HYPOTHALAMUS The thalamus selects incoming sensory impulses and relays them to the cerebral cortex The hypothalamus is important in maintaining homeostasis The limbic system produces emotional feelings and modifies behavior

Limbic System The limbic system is the center of emotions, of pain and pleasure The limbic system is a loose term for a collection of parts found in the diencephalon: Hypothalamus: already defined Hippocampus: associated with MEMORY Working memory: short term memory (like RAM in a computer) Declarative memory: long term memory (like hard drive on a computer) Procedural memory: habits, actions, and skills learned by repetition Amygdala: associated with FEAR and ANGER Flight or fight reflex Arousal Hormonal secretions

PARTS OF THE Brain, cont. 3. Brain Stem The brain stem extends from the base of the brain to the spinal cord and consists of the MIDBRAIN, PONS, and MEDULLA OBLONGATA The MIDBRAIN contains reflex centers associated with eye and head movements The PONS transmits impulses between the cerebrum and other parts of the nervous system and contains centers that help regulate rate and depth of breathing The MEDULLA OBLONGATA transmits all ascending and descending impulses and contains several vital and non-vital reflex centers.

Parts of the Brain, cont. 4. Cerebellum The cerebellum consists of two hemispheres connected by the VERMIS A thin cortex of gray matter surrounds the white matter of the cerebellum The cerebellum functions primarily as a reflex center, coordinating skeletal muscle movements and maintaining equilibrium.

Parts of the Brain, cont. 5. Basal Ganglia Basal ganglia are masses of gray matter located deep within the cerebral hemispheres. They relay motor impulses originating in the cerebral cortex, and aid in controlling motor activities.

Peripheral Nervous System The peripheral nervous system consists of cranial and spinal nerves that branch out from the brain and spinal cord to ALL BODY PARTS It can be subdivided into SOMATIC and AUTONOMIC portions

Nerve Fiber Classification Nerves can be classified as: SENSORY NERVES—conduct impulses into the brain or spinal cord MOTOR NERVES—carry impulses to muscles or glands MIXED NERVES—include both sensory and motor fibers

Somatic--Cranial Nerves TWELVE PAIRS of cranial nerves connect the brain to parts in the head, neck, and trunk Most cranial nerves are mixed, but some are pure sensory or motor nerves The names of the cranial nerves indicate their primary functions or the general distributions of their fibers EX: Olfactory nerves deal with the sense of smell and contain only sensory neurons. Optic nerves deal with vision.

Somatic--Spinal Nerves THIRTY-ONE pairs of spinal nerves originate from the spinal cord These mixed nerves provide a two-way communication system between the spinal cord and the upper limbs, lower limbs, neck, and trunk  Spinal nerves are grouped according the levels from which they arise, and they are numbered sequentially: CERVICAL NERVES (C1-C8) THORACIC NERVES (T1-T12) LUMBAR NERVES (L1-L5) SACRAL NERVES (S1-S5) COCCYGEAL NERVES (Co)

Autonomic PNS The autonomic nervous system functions without conscious effort  It is concerned primarily with regulating visceral activities that maintain homeostasis

General Characteristics Autonomic functions are reflexes controlled from centers in the hypothalamus, brain stem, and spinal cord Autonomic nerve fibers are associated with ganglia where impulses are integrated before distributions to effectors The integrative function of the ganglia provides a degree of independence from the CNS The autonomic nervous system is subdivided into two divisions—sympathetic and parasympathetic The sympathetic division prepares the body for stressful and emergency conditions  The parasympathetic division is most active under ordinary conditions and counterbalances the effects of the sympathetic division after a stressful state.

Sympathetic Nervous System Parasympathetic Nervous System