Central Nervous System Peripheral Nervous System Autonomic Nervous System Nervous System

The neuron Sensory neuron- transmits from sensory receptors to otherneurons Motor neuron- transmits impulses from the CNS to muscles or glands Relay neuron also called interneuron. Located in the CNS and carry impulses from sensory to motor neurons (as in reflexes) Reflex arcs – link the 3 types of neurons

Parts of neuron Cell body – contains cytoplasm, nucleus, and organelles Dendrites - convey signals to cell body Axon – conducts impulses away from the cell body; wrapped in Schwann cell layers in an insulating myelin sheath Synaptic terminals – tips of axon that release neurotransmitters neurotransmitters are the chemicals that cross the synapse to relay an impulse

The Neuron

Central Nervous System CNS made up of the brain and spinal cord Meninges- protective covering Brain- gray matter on outside and white matter on inside Major Regions of Brain: 1. cerebrum 2. diencephalon 3. brain stem (midbrain, pons, and medulla) 4. Cerebellum Cerebrospinal fluid- circulation of hormones, nutrients, and WBC’s in CNS; absorbs shock

Ventricles of the Brain

Cerebrum areas

Cerebral hemispheres Corpus Callosum- connects left and right hemispheres Makes up about 83% of the total brain mass Forms the superior portion of the brain 3 parts of a hemisphere: cortex, white matter, and basal nuclei (ganglia) The surface is covered with ridges called gyri and shallow groves called sulci Sulci divide the 5 lobes: frontal, parietal, temporal, occipital, and insula Larger groves called fissures separate the larger regions Longitudinal fissure separates the left and right hemispheres Transverse cerebral fissure separates the cerebellum from the cerebral hemispheres

Cerebral hemisphere: general Cerebral Cortex 40% of Brain mass – 10 billion cells arranged in 6 layers Gray matter is only 2-4 mm thick 3 kinds of functions: motor, sensory, and association Each hemisphere controls the opposite side of the body, contralateral Although roughly the same in structure, function of the two hemispheres is specialized The cortex works as one unit even though there are functional areas

3 regions of cortex Motor - involved in integration of the activities of the skeletal muscles 4 areas of Motor Cortex: 1. Primary motor cortex- controls the skeletal movements 2. Premotor cotex- controls learned motor skills of a repetitious or patterned nature, like music, typing, and sports related skills 3. Broca’s area- speech 4. Frontal eye field- voluntary movement of eye

Motor cortex and Sensory cortex

3 regions of cortex Sensory - involved with reception of touch, taste, temperature, and pain 1. Primary somatosensory cortex 2. Somatosensory association cortex 3. Visual areas- processes signals felayed from sensory neurons of the eye 4. Auditory areas-pitch, loudness, and location of sound 5. Olfactory cortex- smell 6. Gustatory- taste 7. Visceral sensory- conscious perception ex. Upset stomach, full bladder, need to breath 8. Vestibular cortex - equilibrium

3 regions of cortex Association – more complex than motor or sensory This area receives multiple sensory inputs and sends out multiple motor impulses The anterior portion is involved in intellect, complex learning, recall and personality, abstract ideas, judgment, working memory, reasoning, and planning Posterior portion (temporal, parietal, and occipital lobes) plays a role in recognizing patterns and faces, as well as putting yourself in perspective with your surroundings. It takes different sensory inputs and synthesizes them into a coherent whole.

Differences between 2 hemispheres Left hemisphere is dominant in most people Damage to right brain results in perceptual and spatial disorders Musical ability resides in the right brain Acquisition of different functions by the 2 sides increases functional capacity of brain, without increasing its size Left side is utilized when you compose a sentence, balance a check book, and memorize a list Right side is more free-spirited, visual-spatial, intuition, emotion, artistic and musical, poetic and creative

Cerebral White Matter Responsible for communication between cerebral areas and the lower CNS Consists of myelinated fibers bundeled into large tracts Three tracts: commissures, association, and projection commissures- connect the hemispheres ( corpus callosum) association- connect the lobes of the cortex projection- connect the cortex to the rest of the bodys nervous system

2 nd region - Diencephalon Thalamus- largest region of the diencephalon, deep within the brain; plays a key role in mediating sensation, motor activities, arousal, learning, and memory, “the gateway” to the cerebral cortex. Hypothalamus – found below the thalamus it caps the brain stem. The main control center of the body and is vital to overall homeostasis; autonomic control, emotional response, body temp regulation, food intake regulation, regulation of water balance and thirst, sleep-wake cycle, and endocrine function Epithalamus- most dorsal portion of the diencephalon, contains the pineal gland which secretes melatonin a sleep-inducing signal and antioxidant. It works with the hypothalamus to regulate the sleep-wake cycle.

Diencephalon

3 rd region- Brain Stem Made up of the midbrain, pons, and medulla oblangada Accounts for only 2.5 % of the total brain mass Deep gray matter surrounded by white matter produce the programmed behaviors necessary for survival Found between the cerebrum and spinal cord

Brain Stem Midbrain- Superior colliculi- visual reflex center, coordinate head and eye movements Inferior colliculi- auditory relay from the hearing receptors of the ear to the sensory cortex, reflex in response to sound (startle)Pons- Pons- assist the medulla with breathing, connect brain centers to spinal cord, act as a relay for “conversation” Medulla Oblangada- inferior part of the brain stem Autonomic reflexes maintaining homeostasis Cardiovascular center Respiratory center Vomiting, hiccupping, swallowing, coughing, and sneezing

Brain Stem

4 th region- Cerebellum Accounts for 11% of the brain mass Located dorsal to the pons and medulla Processes inputs received from the cerebral motor cortex, brain stem, and sensory receptors Provides the precise timing and paterns of skeletal contractions for smooth coordinated movements and agility Ex driving, typing, and playing an instrument Occurs subconciously

Spinal Cord A two way impulse conduction pathway and reflex center Found within the vertebral column Protected by meninges and cerebrospinal fluid Thirty one pairs of spinal nerve roots The cord is enlarged in the cervical and lumbar regions Ascending tracts are sensory Descending tracts are motor

Brain Function Brain Waves and the EEG- patterns of electrical activity are called brain waves, a record of this activity is an EEG. Brain waves are identified by frequency: alpha, beta, theta, delta Epilepsy results from abnormal electrical activity causing involuntary muscle contractions during seizures Consciousness – scale alertness, drowsiness, stupor, coma Based on information processing Fainting is temporary loss of consciousness due to inadequate supply of blood to the brain Coma a person is unresponsive to stimuli

Function cont’d Sleep Wake cycles Sleep a state of partial consciousness from which one can be aroused, 2 types NREM and REM (rapid eye movement) REM is closely tied to emotional stability and makes up about 25% of the sleep cycle Narcolepsy is involuntary lapses into REM sleep and can occur without warning Language- left brain both the Bronca’s and Wernike’s areas process language, but the Right side controls emotional content Memory- recall of one’s thoughts, essential to learning and is part of consciousness, STM and LTM (short and long term) the nature of memory is not completely understood but is closely tied to calcium influx and protein receptors and their binding sites.

Protection of Brain Bone, Meninges, and Cerebrospinal fluid play a role in protection of the brain. Blood-Brain barrier- the capillaries of the brain are impermeable to water-soluble potentially harmful substances, but allows gases, water, and essential nutrients to move in and out to feed the brain cells

What are the effects of … Traumatic Brain Injury Cerebrovascular Accidents Alzheimer’s disease Parkinson’s Disease Huntington’s Disease Spinal Cord Trauma Poliomyelitis ALS – Lou Gehrig’s disease Cerebral Palsy Spina bifida cystica or occultta Psychoses and Neuroses

Peripheral Nervous System PNS Include the following Sensory receptors and sensation Transmission lines the Nerves cranial and spinal Motor endings and motor activity Reflex activity

Sensory receptors and sensation Specialize to respond to environmental changes or stimuli Simple receptors for pain, touch, pressure, temperature in skin, as well as those found in skeletal muscles and tendons and visceral organs Complex receptors are the sense organs, vision, hearing, equilibrium, smell, and taste Classified by stimulus detected: mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors Classified by location: exteroceptors, interoceptors, proprioceptors

Sensation to Perception Sensation is awareness of internal and external stimuli Perception is conscious interpretation of those stimuli 3 levels of sensory integration: receptor, circuit (ascending pathway), perceptual levels (cerebral cortex) Function to transform generator potential to action potential Levels of perception: spinal cord reflexes, nonspecific neurons, and then others to the thalamus

Levels of Motor Control Low- spinal cord and reflex arc Middle- motor cortex High - precommand uses cerebellum and basal nuclei

Components of Reflex arc 1. Receptor: site of stimulus action 2. Sensory neuron: transmits impulse to CNS 3. Integration Center: synapse between a signal neuron and motor neuron, or a more complex network of multiple synapses with a chain of interneurons 4. Motor neuron: conducts impulse from integration center to an effector organ 5. Effector: muscle fiber or gland cell that responds by contracting or secreting - somatic reflex actives skeletal muscle - autonomic reflex activates either smooth, cardiac muscle or a gland

Autonomic Nervous System

Function of ANS The system of motor neurons that innervates smooth and cardiac muscle and glands Signals from visceral organs send impulses to the CNS and the autonomic nerves make adjustments as necessary to ensure optimal support for body activities Sending blood to needy areas Speed or slow heart rate Adjust blood pressure and body temperature Increase or decrease stomach secretions

Neurotransmitters in ANS

Neurotransmitters Two major neurotransmitters: acetylcholine (Ach) and norepinephrine (NE) ACh binds to Cholinergic receptors the effects often are excitation or activation NE binds to Adrenergic receptors the effects vary depending on the target cells Effects are felt from the heart to kidney, lungs to digestive tract, constricts blood vessels of the skin and visceral organs except heart, think “adrenaline rush” ** inhibits insulin secretion by pancreas in order to elevate blood sugar levels, stimulates fat cells to break down fat, and liver to release stored sugars

Parasympathetic vs Sympathetic

Adrenal Medulla Embryologically, sympathetic ganglia and the adrenal medulla arise from the same tissue Sometimes referred to as a “misplaced” sympathetic ganglion, being located atop the kidney not in the CNS The adrenal ganglia releases norepinephrine and epinephrine, stimulating the secretion of adrenaline into the blood from the adrenal gland Produces the excitatory effect

Visceral reflexes Referred pain Visceral sensory neurons share pathways with somatic reflex arcs This becomes an issue when you have a heart attack and the visceral pain travels along the same pathway as somatic pain so the pain is perceived as somatic in origin, radiating to the superior thoracic wall and along the medial aspect of the left arm

Hypertension Results from homeostatic imbalance of the ANS Overactive sympathetic vasoconstictor response promoted by high levels of stress Increases the work load of the heart, causing an enlarged heart which restricts the pumping ability and can lead to heart failure Increases wear and tear on artery walls, this increases risk of a tear causing a stroke, or worse a fatal aorta rupture Treatment involves adrenergic receptor blocking drugs