The Nervous System Two Parts: Central Peripheral Brain and spinal cord Nerves

General Functions Detect internal and external changes Collect sensory information and make decisions that motor functions carry out Respond to external/internal stimuli

Neuron Structure A Neuron includes: Cell body Dendtrites Axon Dendrites and the cell body provide receptor surfaces. A single axon arises from the cell body and may be enclosed in a myelin sheath and a neurilemma.

Neuron Structure Schwann Cells Wind tightly around axons; made up of myelin Nodes of Ranvier Gaps between schwann cells

Function of Neurons Sensory (afferent neurons) = carry nerve impulses from peripheral body parts to brain or spinal cord Interneurons = lie within brain or spinal cord; direct incoming sensory info to appropriate parts for processing and interpretation Motor (efferent neurons) = multipolar and carry nerve impulses out of brain or spinal cord to effectors; contract muscles, secrete hormones, etc

Nerve Impulse Unmyelinated fibers conduct impulses over their entire surfaces. Myelinated fibers conduct impulses more rapidly. Nerves with larger diameters conduct faster than those with smaller diameters.

Neuroglial Cells Fill spaces Support neurons Provide structural framework Produce myelin Carry on phagocytosis.

Types of Neuroglial Cells Microglial cells Support neurons and phagocytize bacterial cells and cellular debris Oligodendrocytes Form myelin within the brain and spinal cord

Types of Neuroglial Cells Astrocytes = found between neurons and blood vessels; help regulate concentrations of nutrients and ions within tissue Ependymal cells = cover specialized brain parts (choroids plexuses) and form inner linings that enclose spaces within the brain (ventricles) and spinal cord (central canal)

The Synapse A junction between two neurons Impulse passes junction via neurotransmitters

Synaptic Transmission Impulses usually travel from a dendrite to a cell body, then along the axon to a synapse. Axons have synaptic knobs at their distal ends, which secrete neurotransmitters

Neurotransmitters After being released, neurotransmitters are decomposed or removed from synaptic clefts.

Types of Nerves Nerves are cord-like bundles of neurons and neuroglia Nerves can be classified as: Sensory nerves = carry impulses to brain or spinal cord Motor nerves = carry impulses to muscles or glands

Meninges Bone and meninges surround the brain and spinal cord. Consist of the dura mater, arachnoid mater, and pia mater

Meninges Dura Mater outermost layer white fibrous connective tissue and blood vessels surrounds the spinal cord and brain

Meninges Arachnoid Mater Middle layer Thin, weblike membrane that lacks blood vessels

Meninges Pia Mater Thin Contains many nerves and vessels that nourish underlying cells of brain and spinal cord

Cerebrospinal Fluid Occupies the space between the arachnoid and pia maters. Sub-Arachnoid Space

Spinal Cord Structure Composed of 31 segments, each of which gives rise to a pair of spinal nerves Has a cervical enlargement and a lumbar enlargement. Cervical = supplies nerves to upper limbs Lumbar = supplies nerves to lower limbs

Spinal Cord Structure Two Grooves Anterior median fissure (deep) Posterior median sulcus (shallow)

Functions of Spinal Cord Provides two-way communication system between the brain and other body parts. Ascending tracts carry sensory impulses to the brain. Descending tracts carry motor impulses to muscles and glands.

The Brain The brain is subdivided into the: Cerebrum Cerebellum Brain Stem

Structure of the Cerebrum Two Hemispheres Connected by Corpus Callosum Deep bridge of nerve fibers

Structure of the Cerebrum Cerebrum Surface: Convolutions (gyri) = ridges on brain Sulcus = shallow groove Fissure = deep groove

Structure of the Cerebrum Cerebral Cortex Thin layer of gray matter near the surface. Covers convolutions and dips into sulci and fissures Contains nearly 75% of all neuron cell bodies in the nervous system

Structure of the Cerebrum White Matter Interneurons Located underneath cerebral cortex Makes up bulk of cerebrum

Structure of the Cerebrum 4 Lobes Frontal Parietal Temporal Occipital

Functions of Cerebrum Provides higher brain functions Motor Functions: control movements Sensory Functions: interpret impulses that arrive from sensory receptors, producing feelings or sensations Association Functions: analyze and interpret sensory experiences and oversee memory, reasoning, verbalizing, judgement, and emotion

Association Areas of Cerebrum

Ventricles and Cerebrospinal Fluid Ventricles are interconnected cavities within the cerebral hemispheres and brain stem. Choroid plexuses in walls of ventricles secrete cerebrospinal fluid

Diencephalon A group of structures that include the following: Thalamus, Hypothalamus, Pituitary Gland, Pineal Gland, and Optic Tract Make up Limbic System Produces emotions and modifies behavior

Diencephalon Structure Thalamus Central relay station for incoming sensory impulses Channels impulses to appropriate regions of the cortex for interpretation

Diencephalon Structure Hypothalamus Maintains homeostasis Regulates heart rate body temp water/electrolyte balance controls hunger/body weight sleep hormone secretion

Diencephalon Structure Pituitary Gland Master Gland All the other endocrine glands depend on its secretions for stimulation Pineal Gland Controls circadian rhythm

Diencephalon Structure Optic Tract Includes optic nerves and optic chiasma (where nerve fibers cross over) Infundibulum Behind optic chiasma to which pituitary gland is attached

Brain Stem Made up of 3 Parts: Midbrain Pons Medulla Oblongata

Brain Stem Structure Midbrain Pons Reflex centers associated with eye and head movements Pons Help regulate breathing

Brain Stem Structure Medulla Oblongata Transmits all ascending and descending impulses Signal cross over here

Brain Stem Structure Medulla Oblongata Visceral Control Cardiac center – alter heart rate Vasomotor center – controls constriction and dilation of blood vessels Respiratory center – acts with pons to regulate breathing

Cerebellum Two hemispheres Functions Coordination of skeletal muscle movements Maintenance of equilibrium

Peripheral Nervous System Nerves that branch out from the CNS and connect it to other body parts.

Peripheral Nervous System Two Parts: Somatic = cranial, spinal nerves that connect CNS to skin and skeletal muscle; oversees conscious activities Autonomic = connect CNS to viscera (organs) controls unconscious activities

Somatic Nervous System Cranial Nerves 12 pairs of nerves that emanate from the nervous tissue of the brain.   Exit/enter the cranium through openings in the skull.

Somatic Nervous System Numbers of Spinal Nerves 8 pair of Cervical 12 pair of Thoracic 5 pair of Lumbar 5 pair of Sacral 1 pair of Coccyx

Somatic Nervous System Spinal Nerves Originate from spinal cord Mixed nerves that provide 2-way communication between spinal cord and upper and lower limbs, neck, and trunk

Spinal Nerves Two Parts: Dorsal Root Ventral Root Sensory (afferent root of spinal nerve) Ventral Root Motor (efferent root of spinal nerve)

Spinal Nerves The lumbar, sacral, and coccyx nerves descend beyond the end of the cord, forming a structure called the Cauda Equina which means horse’s tail.

Autonomic Nervous System Functions without conscious effort Regulates the visceral activities that maintain homeostasis

Autonomic Nervous System Two Divisions: Parasympathetic respond to ordinary conditions Sympathetic responds to stressful and emergency conditions