The Nervous System and Endocrine System

Compare and contrast Both transmit signals to other areas of the body Nervous system Very rapid Uses neurons to relay electrical and chemical signals Controls all of the body (everything that the body does) Endocrine System Slower Uses glands and hormones secreted into the blood vessels Controls certain bodily functions (growth, metabolism, sexual development, use of minerals and other substances)

The Nervous System Group of organs that controls the body Thought, movement, and all life processes Responds to external stimuli Information gathered through the senses Stimulus-something that causes a response Very fast Information can pass in less than a second 2 parts: Central Nervous System Brain and spinal cord Peripheral Nervous System Rest of the body

Neurons Cells of the nervous system 3 main parts: Cell Body Contains the nucleus and organelles Dendrite Receive information from neighboring cells Axon Transmits information to other cells 3 Types of Neurons: Sensory neurons-Gather information Interneurons- Receive and relay information to and from CNS Motor neurons-Pass information from CNS to tissues

Transmission of Information Uses a concentration difference of ions (charged atoms) to create electrical signals through the neuron Synapse Area between neurons Information leaves one neuron through the axon and crosses a synapse to the dendrite of another neuron The information is in the form of chemical signals called neurotransmitters

The Senses The only way to gather information about your surroundings Maintain homeostasis Shiver when cold, sweat when hot, eyes dilate in dim lighting, etc. 5 senses: Sight Hearing Smell Taste Touch

Vision Most used sense for humans The eye is the sensory organ Contains photoreceptors (rods and cones) Uses reflected light The eye is covered with a protective layer called the cornea Muscles around the iris (the colored portion) control the size of the pupil (the black circle), controlling how much light enters the eye From the pupil, light passes through a lens, which focuses light on the back of the eye (retina) Rods and cones on the retina generate nerve impulses that travel through the optic nerve to the brain

Vision Problems Nearsightedness (myopia) Eyes focus on close objects, but not on far away ones Light is focused in front of the retina Farsightedness (hyperopia) Eyes focus on far objects, but not close ones Light is focused behind the retina Astigmatism Irregular curvature of the eye Scatters light so that it hits multiple areas on the retina All are easily corrected with lenses (glasses and contacts)

Hearing The ear is the sensory organ Contains auditory receptors called hair cells Ear has 3 parts: Outer ear Part we see is called the pinna Pinna collects sound waves and focuses them into the auditory canal At end of the auditory canal is the tympanic membrane (eardrum), which vibrates Middle ear 3 bones (malleus, incus, stapes) are vibrated by Tympanic membrane and amplify sound Inner ear Amplified sound enters fluid-filled cochlea, which contain hair cells The hair cells bend as fluid moves, creating nerve impulses Impulses travel through auditory nerve to brain

The ear and balance The semicircular canals (part of the cochlea) are also filled with fluid As you move, the fluid moves and stimulates hair cells in the semicircular canals They transmit impulses to the brain, which interprets them and orients your body

Smell and Taste Closely related senses Each have chemoreceptors that detect molecules The ones on your tongue are called taste buds The chemoreceptors generate impulses that pass through nerves to the brain

Touch Sensed in the epidermis and dermis of the skin Mechanoreceptors Some are sensitive to light tough Some are sensitive to pain Some are only sensitive to deep touch Some are wrapped around hair follicles and sense hair movement

The Brain and Spinal Cord Part of the CNS Made up of neurons orientated in a pattern Dense portions of cell bodies are called gray matter Dense portions of axons are called white matter In the brain, gray matter is on the outside In the spinal cord, gray matter is on the inside 3 layers of tissue protect the brain Called meninges If this becomes inflamed, it is meningitis Brain divided into 3 main parts

Cerebrum Largest portion Interprets signals from the body Emotion, needs, motion, pain 2 hemispheres connected by nerves Each controls the opposite side of the body The thick band of nerves connecting the hemispheres is called the corpus callosum Outer layer of the cerebrum is the cerebral cortex (folded portion) Areas of the cerebral cortex that do a task are called lobes 4 main lobes Frontal: Planning, personality, reasoning, judgement, voluntary motion, speech (Broca’s area) Parietal: Touch and language processing Occipital: Vision Temporal: Speech interpretation, hearing, memory

Cerebellum Coordinates movement Maintain posture and balance Muscle memory

Brain Stem Connects brain to spinal cord Controls involuntary actions Reflexes

Spinal Cord Connects brain to rest of body Delivers messages to muscles Damage to spinal cord can lead to paralysis Disconnects neurons from the brain Reflexes pass to the spinal cord, then back to the muscle Does not need to travel through the brain, so quicker

Peripheral Nervous System Connect CNS to rest of body 2 parts: Somatic Nervous System Controls voluntary movement Autonomic Nervous System Controls involuntary movement 2 parts: Sympathetic Nervous System-”fight or flight” response Parasympathetic Nervous System-calms body

Important Neurotransmitters Dopamine-Role in emotion, stress, and voluntary muscle movement Serotonin-Role in emotion, muscle, and hunger Homeostasis is maintained if the levels are correct Incorrect levels of dopamine affect muscles Can lead to Parkinson’s Disease and Schizophrenia Incorrect levels of serotonin can lead to anxiety and depression

Drugs and the Brain Drugs alter the release of neurotransmitters Can train your body to depend on them Called addiction When the drug is stopped, the body senses something is wrong and leads to the effects of withdrawal Stimulants increase the release of neurotransmitters Depressants reduce the release of neurotransmitters, or block the receptors

The Endocrine System Group of glands that release chemical messages into the blood Called hormones 2 categories of hormones Steroid hormones Attach to DNA Nonsteroidal hormones Chemical reaction in cytoplasm Attach to target cells

Main Endocrine Glands Hypothalamus Found in brain Causes release of growth hormones and control the reproductive system Controls the pituitary gland Pituitary Gland Also found in brain Releases growth hormone and causes blood to absorb water from the kidneys Also controls function of other glands

More Endocrine Glands Thyroid In throat Controls metabolism Parathyroid On thyroid Controls how the body uses calcium Thymus In chest Causes WBCs to mature and reproduce Adrenal Glands In torso above kidneys Help respond to stress (“fight or flight”)

Last of the Endocrine Glands Pancreas Between stomach and intestines Controls the use of glucose Produces insulin Gonads Ovaries in females and testes in males Estrogen in females and testosterone in males Release sex hormones, controls production of gametes, development of sex characteristics

Feedback Loops Positive Feedback The production of a hormone causes more to be released Not as common Childbirth Negative Feedback The production of the hormone stops hormone release Most common in body