Nervous System

The Human Nervous System consists of the Central Nervous System & the Peripheral Nervous System

Nerve Cells Neurons – Basic functioning units of the nervous system

Neurons Made up of a cell body and branches called dendrites and axons – Dendrites receive messages from other neurons and send them to the cell body – Axons carry messages away from the cell body

Any message carried by a neuron is called an impulse

Neurons A message carried by a neuron is called an impulse

Types of Neurons Sensory Motor Interneuron

Central Nervous System 1 - BrainBrain 2 - Spinal cord

Peripheral Nervous System 1 - Cranial nerves (12 pair) & their branchesCranial nerves 2 -Spinal nerves (31 pair) & their branches nerves

Divisions of the Human BrainDivisions of the Human Brain: 1 - Myelencephalon, which includes the medullaMyelencephalon 2 - Metencephalon, which includes the pons and cerebellum 3 - Mesencephalon, which includes the midbrain (tectum and tegmentum) 4 - Diencephalon, which includes the thalamus and hypothalamus 5 - Telencephalon, which includes the cerebrum (cerebral cortex, basal ganglia, & medullary body)

The divisions of the brain include the (1) cerebrum, (2) thalamus, (3) midbrain, (4) pons, and (5) medulla oblongata. (6) is the top of the spinal cord

Divisions of Peripheral Nervous System Somatic - supplies & receives fibers (neurons) to & from the skin, skeletal muscles, joints, & tendons Autonomic Nervous System - Visceral - supplies & receives fibers to & from smooth muscle, cardiac muscle, and glands The ANS has two divisions : – Parasympathetic – Sympathetic division

Brain

Medulla 1- continuous with spinal cord 2 - contains ascending & descending tracts that communicate between the spinal cord & various parts of the brain 3 - contains 3 vital centers: cardioinhibitory center, which regulates heart rate respiratory center, which regulates the basic rhythm of breathing vasomoter center, which regulates the diameter of blood vessels 4 - origin of five cranial nerves (VIII or vestibulocochlear, IX or glossopharyngeal, X or vagus, XI or accessory, & XII or hypoglossal

Brain Stem The brain stem is the region between the diencephalon (thalamus and hypothalamus) and the spinal cord It consists of three parts: midbrain, pons, and medulla oblongata. The midbrain is the most superior portion of the brain stem. The pons is the bulging middle portion of the brain stem. This region primarily consists of nerve fibers that form conduction tracts between the higher brain centers and spinal cord. The medulla oblongata, or simply medulla, extends inferiorly from the pons. It is continuous with the spinal cord at the foramen magnum. All the ascending (sensory) and descending (motor) nerve fibers connecting the brain and spinal cord pass through the medulla

Pons 1 - Bridge connecting spinal cord w/ brain & parts of brain w/ each other 2 - Origin of four cranial nerves (V or trigeminal, VI or abducens, VII or facial, & VIII or vestibulocochlear) 3 - contains pneumotaxic center (a respiratory center)

Midbrain 1 - Corpora quadrigemina - visual reflexes & relay center for auditory information.Two pairs of rounded knobs on the upper surface of the midbrain mark the location of four nuclei, which are called collectively the "corpora quadrigemina." These masses contain the centers for certain visual reflexes, such as those responsible for moving the eyes to view something as the head is turned. They also contain the hearing reflex centers that operate when it is necessary to move the head so that sounds can be heard better.Corpora quadrigemina 2 - Cerebral peduncles - ascending & descending fiber tractsCerebral peduncles 3 - Origin of two cranial nerves (III or oculomotor & IV or trochlear)

1- posterior medullary velum, 2 - choroid plexus, 3 - cisterna cerebellodellaris of subarachnoid cavity, 4 - central canal, 5 - corpora quadrigemina 6 - cerebral peduncle, 7 - anterior medullary, 8 - ependymal lining of ventricle, 9 - cisterna pontis of subarachnoid cavity

Thalamus Relay station for nearly all sensory impulses (except olfaction)

HypothalamusHypothalamus Control of Autonomic Nervous System 2 - Reception of sensory impulses from viscera 3 - Intermediary between nervous system & endocrine system 4 - Control of body temperature 5 - Regulation of food intakeRegulation of food intake 6 - Thirst centerThirst center 7 - Part of limbic system (emotions such as rage and aggression) 8 - Part of reticular formation

Reticular formationReticular formation portions located in the spinal cord, medulla, pons, midbrain, & hypothalamus 2 - needed for arousal from sleep & to maintain consciousness The ascending reticular activation system. During periods of wakefulness, impulses from the brainstem activate neurons in the thalamus that are crucial for transmitting information to the cerebral cortex. Impulses also travel to the hypothalamus and throughout the cerebral cortex. A key switch in the hypothalamus (SCN, or suprachiasmic nucleus) that serves as the brain's 'master clock' shuts off this arousal system during sleep

CerebellumCerebellum - functions in coordination, maintenance of posture, & balance

Cerebrum 1 - largest portion of the human brain 2 - consists of 2 hemispheres divided by a fissure 3 - includes cerebral cortex, medullary body, & basal ganglia: – Cortex: outer mm of the cerebrum consists of gray matter (cell bodies & synapses; no myelin)gray matter 'folded', with upfolded areas called gyri & depressions or grooves called sulcigyrisulci consists of four primary lobesfour primary lobes

'Forward' (a) and 'inverse' (b) model control systems for movement. According to 'instructions' from the premotor cortex (P), an area in the motor cortex (controller, or CT) sends impulses to the controlled object (CO; a body part). The visual cortex (VC) mediates feedback from the body part to the motor cortex. The dashed arrow indicates that the body part is copied as an 'internal model' in the cerebellum. In the forward-model control system, control of the body part (CO) by the motor cortex (CT) can be precisely performed by referring to the internal feedback. In the inverse-model control system, feedback control by the motor cortex (CT) is replaced by the inverse model itself

Medullary body: the 'white matter' of the cerebrum; consists of myelinated axons types of axons include: – commissural fibers - conduct impulses between cerebral hemispheres (and form the corpus callosum) commissural fibers – projection fibers - conduct impulses in & out of the cerebral hemispheres – association fibers - conduct impulses within hemispheres

Basal ganglia masses of gray matter in each cerebral hemisphere important in control of voluntary muscle movements

Limbic System 1 - consists of a group of nuclei + fiber tracts 2 - located in part in cerebral cortex, thalamus, & hypothalamus 3 - Functions: – aggression – fear – feeding – sex (regulation of sexual drive & sexual behavior)

Spinal cord

The spinal cord extends from the skull (foramen magnum) to the first lumbar vertebra. Like the brain, the spinal cord consists of gray matter and white matter. The gray matter (cell bodies & synapses) of the cord is located centrally & is surrounded by white matter (myelinated axons). The white matter of the spinal cord consists of ascending and descending fiber tracts, with the ascending tracts transmitting sensory information (from receptors in the skin, skeletal muscles, tendons, joints, & various visceral receptors) and the descending tracts transmitting motor information (to skeletal muscles, smooth muscle, cardiac muscle, & glands). The spinal cord is also responsible for spinal reflexeswhite matter of the spinal cordascending and descending fiber tracts

Reflex rapid (and unconscious) response to changes in the internal or external environment needed to maintain homeostasisexternal environment Reflex arc - the neural pathway over which impulses travel during a reflex. The components of a reflex arc include: Reflex arc 1 - receptor - responds to the stimulus 2 - afferent pathway (sensory neuron) - transmits impulse into the spinal cord 3 - Central Nervous System - the spinal cord processes information 4 - efferent pathway (motor neuron) - transmits impulse out of spinal cord 5- effector - a muscle or gland that receives the impulse from the motor neuron & carries out the desired response