Nervous System

Neurology – study of the nervous system nervous & endocrine systems work together to maintain homeostasis

Nervous System – works very fast Uses electrical signals called nerve impulses Short-lived responses Ex.; knee jerk reflex Endocrine system – works slowly Uses chemical messengers called hormones Responses last a long time Ex.; reproductive cycle

Nervous System Vocab neuron – cell of the nervous system Nerve – bundle of neurons with connective tissue & blood vessels Cranial nerves – 12 pair; nerves originating from the brain (mainly sensory & facial motor) Spinal nerves – extend from spinal cord to supply specific body regions Ganglia – a group of nerve cell bodies Plexus – network of neurons supplying the same area Sensory receptors – detect stimuli in internal & external environment (pain, pressure, etc)

Functions of the Nervous System 1. Sensory Detect stimuli; Sensory (afferent) neurons carry this info to the brain 2. Integrative Processes information; Interneurons (associative neurons) analyze & store info, make decisions 3. Motor Respond to stimuli; Motor (efferent) neurons carry info from brain & spinal cord to effects (cells & organs that are acted on)

Branches of the Nervous System 1. Central Nervous System (CNS) Source of thoughts, emotions, memories Includes brain and spinal cord 2. Peripheral Nervous System (PNS) Relay station to CNS Includes all nervous tissue outside CNS (ex.; sensory/motor neurons) Further divided into Somatic, Autonomic and Enteric Nervous Systems

Somatic Nervous System (SNS) Under voluntary control Sensory neurons send message to brain Motor neurons send impulses to skeletal muscle only

Autonomic Nervous System (ANS) Involuntary Sensory receptors located in chest & abdomen Motor neurons send message to smooth & cardiac muscle Has sympathetic & parasympathetic division Sympathetic – stimulates functions Parasympathetic – inhibits functions

Enteric Nervous System (ENS) Brains of the gut Involuntary Controls digestive system

Types of Nerve Cells 1. neurons – functional cell of the nervous system Soma – cell body Dendrites – “little tree”; receives message Axon – carries message to next neuron, muscle, etc. 2. neuroglia – “glue” of nervous system Schwann cell – found in PNS; encircles axon & produces myelin sheath Oligodendrocyte – found in CNS; myelinates neurons

Coverings of Nerves Myelin – insulating tissue that speeds up nerve impulses (not on all nerves) Composed of lipids Nodes of Ranvier – gaps in between myelinated sections Infants have slow/uncoordinated responses due to incomplete myelin sheath formation Neurolemma – covering of myelin sheath only in PNS; helps regenerate an injured axon Since CNS neurons lack neurolemma, they cannot regenerate after an injury

The Brain Portion of the central nervous system protected by the cranium Made of 100 billion neurons Weighs ~ 3 lbs Uses only glucose for energy Different regions of the brain are specialized for different functions

Coverings of the Brain Brain is surrounded by 3 layers of cranial meninges 1. dura mater – tough, outer layer (leather-like) 2. arachnoid – middle layer; has a spider-web appearance 3. pia mater – innermost layer that adheres to the brain

Cerebrospinal fluid Clear, colorless liquid that circulates continuously in the subarachnoid space around the brain and spinal cord Function is to act as a shock absorber and for the exchange of nutrients/wastes Provides optimal environment for nerve impulses to travel

Blood supply to the brain Brain is 2% of body mass but receives 20% of blood flow because it can’t store glucose Blood-brain barrier – protects brain cells from harmful substances Glucose, O 2, CO 2, anesthesia, alcohol readily pass from blood into brain Proteins & antibiotics do not cross Lack of O 2 for 4 minutes = permanent brain damage

Parts of the Brain 1. Cerebrum – the “seat of intelligence” Forms the bulk of the brain Longitudinal fissure – splits cerebrum into right & left hemispheres, which control opposite sides of the body Corpus callosum – connects hemispheres internally; where nerves cross to opposite

Cerebral cortex – consists of grey matter (superficial) during embryonic development, grey matter develops faster than the deeper white matter, so it folds upon itself Gyri – folds (gyrus – singular) Fissures – deep grooves between folds Sulci- shallower grooves (sulcus – singular) Each hemisphere is divided into four lobes

Lobes of the cerebrum A. frontal lobe – responsible for concentration, problem-solving, planning, & formation of speech Contains pre-central gyrus – motor area controlling voluntary skeletal muscles B. parietal lobe – sensory area for skin, interprets sensory info; storage of memories of past sensory experiences

C. Occipital lobe – responsible for combining visual images and visual recognition D. Temporal lobe – olfactory (smell) and auditory info Memory of visual and auditory patterns Understanding speech (translating words to thoughts), addition of emotion to speech

2. Cerebellum – posterior portion of the brain Information about body position Coordination of complex skeletal movements posture

3. Diencephalon – extends from the brain stem to the cerebrum; 3 main parts A. Thalamus – relay station for all impulses to cerebrum; essential role in awareness and acquisition of knowledge B. hypothalamus – control center of autonomic nervous system (ANS) Controls pituitary gland, regulates emotional & behavioral patterns, eating & drinking, circadian rhythms & consciousness, & controls body temp C. pineal gland – secretes melatonin (promotes sleep)

4. Brainstem – continuous with the spinal cord; 3 main parts A. midbrain – controls reflexes & eye movement B. pons – relays sensory information from peripheral nerves to cerebellum & cerebrum Regulates rate & depth of breathing with the medulla C. medulla oblongata – controls heart and breathing rate Controls smooth muscle contractions

Spinal cord 100 million neurons Connects brainstem at foramen magnum White matter on outside, grey matter on inside Spinal nerves exit spinal cord to supply specific regions of the body Ends between 1 st & 2 nd lumbar vertebrae Ends of nerves branch into cauda equina (horse’s tail)