 600 mya = sponges have different tissues  550 mya = flatworm with “eyespots’  500 mya = first fish  360 mya = reptiles w/lower brains  65 mya = mammals with newer brain areas  Evolution has had half a billion years to improve on the early fish nervous system

 Divided into two parts: 1. Central Nervous System (CNS): Brain and Spinal Cord 2. Peripheral Nervous System (PNS) Cranial Nerves and Spinal Nerves

 The nervous system is made up of nerve cells called neurons  They assist the nervous system in communication within the body, coordination of body activities, orientation to the environment, and assimilation of information

 Schwann Cells and oligodendrocytes = produce myelin. Myelin insulates neurons and increase speed of conduction  Astrocytes = maintain synaptic environment, and help repair damage

 Sensory neurons (afferent): Found in skin or sensory organs and help carry messages to the spinal cord and brain.  Motor neurons (efferent): Helps carry messages from the brain and spinal cord to the muscles and glands.  Associative neurons (interneurons): Help carry messages from sensory neurons to the motor neurons.

 A synapse is the space between two communicating neurons (about 1 micron)  Messages are passed from the terminal branch or synaptic knob of one cell to the dendrite of another.  Neurotransmitters are released and cross the synaptic cleft.

Action Potential = The transmission of an electrical impulse Neurons are negatively charged cells when at rest. When stimulated, Positively charged ions rush in (depolarization) If there is enough depolarization (Threshold Level) then the action potential travels the length of the neuron

 The human brain weighs about 3 lbs and consists of over a 100 billion neurons.  The brain is protected by the skull and three membranous coverings called meninges  The outer cortex is known as the cerebral cortex

 The meninges consists of three layers  The outermost covering is called the dura mater  The middle layer is called the arachnoid  Covering the brain itself is the pia mater

Deep within the brain 4 lined cavities filled with cerebrospinal fluid Cerebrospinal fluid acts as a shock absorber The fluid is formed by filtration from the choroid plexuses The fluid transports nutrients and removes waste products from brain cells 11-4

 The brain itself can be divided into 4 main parts 1. Cerebrum – 2 hemispheres which are made up of the 5 lobes of the brain 2. Diencephalon – controls sensory impulses and homeostasis 3. Cerebellum – aka “mini-brain”; controls movement and coordination 4. Brainstem – controls the more primitive functions like heart rate and breathing

 Largest part of the brain (~2 lbs)  Made up of two hemispheres that are connected by a bundle of nerve fibers called the corpus callosum This allows the hemispheres to communicate with each other

 Frontal: personality, problem solving, impulse control, decision making, reasoning, planning, motor function  Parietal: sensation and perception, integrating sensory information  Temporal: auditory sensation, verbal communication  Occipital: visual perception  Limbic Lobe or System: emotion and regulation of homeostasis

 Thalamus: Acts as a relay station for incoming and outgoing nerve impulses. Damage to this area may result in increased sensitivity to pain.  Hypothalamus: Considered the “brain” of the brain. Stimulates the release of hormones as well as help sustain homeostasis and play a role in the display of emotions.

 Controls all functions that have to do with skeletal muscles.  This includes: Body orientation (balance) Muscle tone Coordination of muscle movements (speaking, walking, writing, etc.)

 Pons: Serves as a two-way conductive pathway for nerve impulses.  Midbrain: Contains reflex centers for vision and hearing.  Medulla oblongata: A pathway between the brain and the spinal cord. Contains neurons for vital functions such as heart rate, respiration, blood pressure, and swallowing and vomiting.

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