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The Nervous System Medical Term “Neuro” Overview • The entire nervous system relies on the transmission of electrical impulses – These impulses are done by neurons, the operating cells of the brain and spinal cord • Nervous impulses travel from neuron to neuron as they send information from one area of the body to another. • The speed is almost instantaneous! (268 miles/hour) Different parts of the Nervous System • Central Nervous System (CNS) – Network of nerve tissue (neurons) found in the brain and spinal cord • Peripheral Nervous System (PNS) – All nerve tissue (neurons) outside the brain and spinal cord. They include: • 12 Cranial (head) nerves that enervate the head/senses • 31 pairs of spinal nerves that enervate the arms, trunk, and legs Motor vs Sensory • • Fundamental understanding of nervous system Sensory Nerves (“you sense”) – – These nerves receive sensory info from the body Also known as Afferent Nerves • • • • Motor Nerves (“you move”) – – The brain sends out impulses to muscles Also known as Efferent Nerves • • • • e.g. smell, taste, touch, sight Breeze against your face That impulse is sent from the nerves in your body to your brain via the spinal cord You move your arm You blink e.g. Burning your hand on the stove. Most nerves are both sensory and motor Neurons • Neurons – Cells responsible for electrical transmission – The brain, spinal cord, and nerves are all comprised of neurons – 100 billion neurons just in brain 3 Major Parts of the Neuron • 1. Cell Body – Contains nucleus and organelles. • 2. Dendrites – Short, stubby branches that carry impulses to the cell body from another neuron – They are the “receiving” part of neuron • 3. Axons – Long extension that carries impulses from the cell body – They transmit impulses to dendrites of the next neuron. – They are the “giver” part of a neuron. – Axons are surrounding by fat which helps accelerate the electrical impulse. Neurons (cont) • Synapse – Open area where the axon of one neuron communicates with the dendrite of the next one. – Neurotransmitter • The Chemical released there to send the “message” across • Famous neurotransmitters – – – – Epinephrine (Adrenaline) Dopamine Serotonin Acetylcholine Glial Cells • • • Glial cells are the “bodyguards” of neurons They are not responsible for electrical impulse Their job is to: – Surround the neurons to anchor them in place – Produce the fat (myelin) of the axon to speed transmission – Destroys pathogens – Supplies nutrients to neurons. Activity • Get into your groups – Write down 10 examples of sensory impulses – Write down 10 examples of motor impulses The Brain The Brain • Responsible for every physical and mental activity of the body – Memory, emotion, thought, judgment, reasoning, consciousness, etc. – It is made of white and grey matter • • • • Comprised of mostly fat Protected by the cranium Weighs 3 pounds The four major structures of the brain – – – – 1. Cerebrum 2. Cerebellum 3. Diencephalon 4. Brain Stem 1. Cerebrum • Largest and uppermost part of brain – It has 2 hemispheres (left and right) – Corpus Callosum- joins hemispheres together and quickens communication b/t the two sides. – Left side of cerebrum focus on logic and reason – Right side focus on creativity – Gyri (sing. gyrus) are the folds or mountains on the cerebrum – Sulci (sing. sulcus) are the dips or cracks on the cerebrum. Arrangement of Neurons • Most neurons in the brain are arranged in either two layouts. • 1) Long layers of neurons – Cerebral Cortex is the outermost layer of the cerebrum made of Grey Matter – Consists of layers of neurons about 4 mm thick – Responsible for thought, awareness, consciousness and learning • 2) Cluster of neurons (aka brain nuclei) – Seen mostly in deeper parts of the brain (hypothalamus, thalamus) Grey vs White Matter • The brain is comprised of Grey Matter and White Matte • Grey Matter is made largely from layers of the bodies of neurons. • White matter is mostly comprised of glia and the long axons of neurons connecting one part of the brain to another. 1. The Cerebrum • Each hemisphere of the cerebrum is divided into 5 lobes – – – – Frontal Parietal Temporal Occipital • These 4 named after the bone that is directly above them • Insula (Limbic) – The inner side of hemisphere that faces the other hemisphere. – Includes Hippocampus Temporal Lobe of Cerebrum • Responsible for hearing • Features the hippocampus – Main area for memory Frontal Lobe of Cerebrum • Responsible for emotions Occipital Lobe of Cerebrum • Responsible for vision processing Parietal Lobe of Cerebrum Limbic Lobe of Cerebrum • Includes the Hippocampus – Responsible for memory and spatial navigation – Alzheimer’s and other forms of dementia affect the Limbic. 2. Diencephalon (Interbrain) • 2 main parts – Thalamus “The Relayer” • Receives all sensory info from the body and sends it to the appropriate part of the brain for processing • Also, it receives impulses from the cerebrum and relays them to various parts of body via efferent motor nerves – The Hypothalamus • Regulates the Autonomic Nervous System (ANS) • Heartbeat, body temperature, smooth muscle control, fluid balance. • Things you can’t control 3. Cerebellum “Baby Brain” • 2nd largest part of the brain • Sits in the posterior portion of the skull, next to occipital bone. • Maintains balance and equilibrium • Coordinates muscular movement 4. Brain Stem • • • • Comprised of: 1. Midbrain 2. Pons 3. Medulla • Brain stem is a pathway for impulse conduction between the brain and spinal cord Are you left or right brained? • Based on this picture, extrapolate 5 characteristics of people who are predominately: – Right-brain – Left-brain Meninges (sing. Meninx) • 3 layers of matter that surround the brain – 1. Dura mater • Hard, fibrous material – 2. Arachnoid Space • Web-like middle space bathed in cerebro-spinal fluid (CSF) – 3. Pia mater • Thin layer actually on the brain – Meningitis-infection of the brain layers. Cerebro-spinal Fluid (CSF) • Syrupy fluid that bathes and protects the brain and spinal cord. • Ventricles – Chambers full of CSF fluid that are inside the brain • Lateral • 3rd Ventricle • 4th Ventricle Spinal Cord • Transmits sensory impulses from the body to the brain, and • Transmits motor impulses from the brain to the body • Located in the spinal cavity of the vertebrae with spinal nerves exiting between each vertebrae to enervate the arms, trunks, and legs. • Spinal cord runs from the brain and to Lumber 3. • Cauda Equina- strands of nerves that run down the Plexus • Big branches of nerves that come off of spinal cord – Brachial • Comes of the spine near lower c-spine • Enervates the upper extremity – Lumbar • Comes off L-spine • Enervates hips, groin, abdominal area – Sacral • Comes off sacrum • Enervates the lower extremity Cranial Nerves • Most important nerves in the body. There are 12 – All originate off the brain stem – Listed in Roman numerals • I-(Olfactory)-Smell • II-(Optic)-Eyesight • III (Oculomotor), IV (Trochlear), and VI (Abducents)-Eye Movement • V (Trigeminal)-Facial Sensation • VII (Facial)-Facial motor • VIII (Vestibulocochlear)-Ear • IX (Glossopharyngeal) and XII (Hypoglossal)- Tongue and Swallowing • X (Vagus) -Controls diaphragm, all organs in body • XI- (Spinal) Pathology • MeningitisInflammation of the meninges • Concussion-Bruising of brain tissue • HydrocephalusSwelling of the brain due to increase amount of CSF fluid • Encephalitis-Infection of the brain, typically Hydrocephalus “Water in the brain” • • • • Excess CSF fluid in the brain The choroid plexus of the ventricles, the cells responsible for producing CSF, either produce too much, or the venous system doesn’t absorb it fast enough It compresses (squeezes) the brain tissue which increases intracranial pressure. Etiology – Mal-development in utero – May develop during adulthood by a tumor, infection, etc • Signs – Disease occurs in infants – Head swells as brain pushes unsutured cranial bones apart – Scalp veins dilate – Decreased mental abilities Hydrocephalus • Diagnosis – Lumbar tap – CT/MRI – Treatment • Shunt – A shunt is a tube inserted in the ventricles to move the excess fluid to the right atrium or abdomen. Seizures • • • • • • Uncontrolled, excessive discharge of neurons Multiple causes and types May be caused by external stimuli, drugs, secondary disease. Generalized seizure- loss of consciousness due to multiple parts of the brain seizing Partial- no loss of consciousness, normally only one part of brain seizes. Petit mal seizure (Generalized) – Occurs in children – Lasts a few seconds, twitches and lip smacking ensue – Child returns to normal c no memory of it • Grand mal seizure (Generalized) – – – – Begins with twitching, nausea, depression Aura-visual or auditory hallucination Loss of consciousness follows The tonic-clonic stage ensues of strong muscle contraction/relaxation as the body contorts itself into strange position. Foaming of the mouth, screaming, and incontinence may ensue. Seizures • Treatment – Anti-convulsive and sedative drugs are given to lessen chance of seizure or to minimize outbursts. Huntington’s Disease • Genetic disorder, 13 from House has it. • Progressive atrophy (or deterioration) of neurons • Ventricles swell • Symptoms: Wild mood swings, wild jerky movements of extremities, gradual loss of cognitive and motor skills • Prognosis: Death! Schizophrenia • Chronic mental condition which features the following symptoms: – Visual and auditory hallucinations – Delusions of personal grandeur – The belief that people are plotting against you. – Detachment, increased drug use, and suicidal ideation. Dissociative Identity Disorder • Formerly Multiple Personality Disorder. • Person has at least 2 distinct personalities (alter egos) • One personality controls the other • Main personality has time of amnesia. • Cause: Trauma (physical/sexual) • Controversy: Herniated Disc • The intervertebral disc is comprised of two components: – Nucleus pulposus- inner gelatinous filling – Annulus fibrosis- tough outer layer – Poor body mechanics, trauma, or degenerative condition cause the nucleus to leak out. – It impinges or touches either the spinal cord or the nerve roots that go down the arm or leg – Causes loss of motor or sensory sensation and intermittent pain in leg or arm (depending on which plexus it is impinging). – Minor day surgery may fix it easily Assignment • Identify the following terms: – Neuron – Dendrite – Axon – Synaptic Gap – Cerebellum – Corpus Callosum