Chapter 3 Neural and Hormonal Systems

Neurons: The Building Blocks of the Nervous System. Nervous system is your body’s electrochemical communication system. Brain tell your body parts to move, your face to express emotion, and your internal organs to go about their business. Your nervous system, in partnership with your sensory systems. Gathers information so your brain can response to stubbed toes, fire alarms, and smell of popcorn.

Tasks of the Neuron Your brain, spinal cord, and nerves are formed form neurons. Neurons are nerve cells; the basic building block of the nervous system. Three tasks To receive information (in the form of electrochemical impulses) from the neurons that feed into it. To carry this information down its length To pass information on the next neurons in line Neurons are so limited in function—their main capability is transmitting an impulse, or “firing”. A neuron is a single cell A nerve is a bundle of neurons.

Parts of a Neuron Dendrites: The bushy, branching extensions of a neuron that receive messages and conduct impulses toward cell body (soma). Soma: The cell body of a neuron, which contains the nucleus and other parts that keep the cell healthy. Axon: The extension of a neuron through which neural impulses are sent. Axon terminal: The endpoint of a neuron, where neurotransmitters are stored.

Review What is a neuron? What are the three tasks of a neuron What is the difference between a neuron and a nerve.

Neural Communication Action potential- a neural impulse; brief electrical charge going down the axon. Ex. Restroom. Refractory period- “recharging phase” when a neuron cannot generate another action potential. Resting potential- neuron is at rest and capable of generating an action potential. All or none principle- if a neuron fires, it always fires at the same intensity; all potentials are same strength. Synapse- tiny, fluid filled gap between the axon terminal of one neuron to dendrite of another. Neurotransmitter- a chemical messenger that travels across the synapses from one neuron to the next; influences whether a neuron will generate action potential.

Neural Chain Receptor cells- specialized cells in the sensory systems; can turn other kinds of energy into action potentials. Sensory nerves- nerves that carry information from the sense receptors to central nervous system. Interneurons- nerve cells in the brain and spinal cord; responsible for processing information Motor nerves- nerves that carry information to the muscles and glands from the central nervous system.

Structure of the Nervous System Central nervous system (CNS)- brain and spinal cord Peripheral nervous system- sensory & motor nerves that connect the central nervous system to the rest of the body. Somatic nervous system- division of peripheral nervous system that controls the body’s skeletal muscles. Autonomic nervous system- part of peripheral nervous system that controls the glands and muscles of internal organs. Sympathetic division- arouses the body to deal with perceived threats Parasympathetic division- part of the autonomic nervous system that claims the body.

The Endocrine System Endocrine system- a set of glands that produce hormones, chemical messengers that circulate in the blood. Hormone- chemical messengers produced by the endocrine glands and circulate in the blood. Pituitary gland- “master gland” that controls other endocrine glands.

Section 2: The Brain

Lower-Level Brain Structures The Brainstem The brainstem is oldest part of the brain and central core. It’s responsible for automatic survival functions. Medulla- base of the brainstem; controls life-support functions like heartbeat and breathing. Reticular formation- plays an important role in controlling wakefulness and arousal. Thalamus Thalamus is the brain’s sensory switchboard; located at top of brainstem; directs messages to the sensory receiving area in the cortex. Cerebellum- is attached to the rear of the brainstem; helps coordinate voluntary movements & balance.

The Limbic system The Limbic system- a ring of structures that borders the brainstem and cerebral cortex; helps regulate important functions such as memory, fear, aggression, hunger, and thirst. Hypothalamus- a neural structure lying below thalamus; directs maintenance activities such as eating, drinking, and body temperature. Hippocampus- a neural center located in the limbic system; it helps process new memories for permanent storage. Amygdala- two-almond neural clusters in the limbic system that are linked to emotions, such as fear and anger.

F.Y.I. How much of the brain we use? The idea the we only use 10% of our brains is a myth that was developed last century. As brain research techniques have evolved, scientists found that most of the brain is active at any given moment. Those areas that were thought to be unused were probably the association areas.

The Cerebral Cortex Cerebral Cortex- intricate fabric of interconnected neural cells that form the cerebral hemispheres; body’s ultimate control and information-processing center. Longitudinal fissure- the long crack that separates the cerebral cortex into the left and right hemispheres. Corpus callosum- large band of neural fibers that connects the 2 brain hemispheres and carries messages between them. Frontal lobes- includes motor cortex; is involved in making plans and judgments. Parietal lobes- includes the somatosensory cortex and general association areas used for processing information. Occipital lobes- includes visual processing areas. Temporal lobes- includes the auditory (hearing) areas. Motor cortex- controls voluntary movements.

Hemispheric Differences Somatosensory cortex- at the front of the parietal lobes that registers and processes body sensations. Broca’s area- usually in the left hemisphere, that directs the muscle movements involved in speech. Wernicke’s area- involved in language comprehension and expression; usually in the left temporal lobe. Plasticity- brain’s capacity for modification, as evident in brain reorganization following damage.

Review Which part of the brain is responsible for hearing? What is the frontal lobes responsible for? What do you think happens when someone gets hit in the back of the head? Why? What is the body’s ultimate control and information-processing center.