human biology ch. 13
The myelin sheath
A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation, and regeneration in the PNS Schwann cells - neuroglia that make up the myelin sheath in the PNS Nodes of Ranvier - gaps between myelination on the axons Saltatory conduction - conduction of the nerve impulse from node to node
What role does ATP play in muscle contraction and rigor mortis?
ATP is needed to attach and detach the myosin heads from actin. After death, muscle cells continue to produce ATP through fermentation and muscle cells can continue to contract. When ATP runs out, some myosin heads are still attached and cannot detach, causing rigor mortis. Rigor mortis and body temperature may be used to estimate time of death.
The nerve impulse: Action potential
Action potential - rapid change in the axon membrane that allows a nerve impulse to occur Sodium gates open, letting Na+ in. Depolarization occurs. Interior of axon loses negative charge (-55 mV, then +35 mV). Potassium gates open, letting K+ out. Repolarization occurs. Interior of axon regains negative charge (-70 mV). Wave of depolarization/repolarization travels down the axon. Resting potential is restored by moving potassium inside and sodium outside.
Examples of how skeletal muscles are named
Attachment - the brachioradialis is attached to the brachium and radius Number of attachments - the biceps brachii has 2 attachments Action - the extensor digitorum extends the digits
Drugs and drug abuse
Both legal pharmaceuticals and illegal drugs of abuse have certain basic modes of action. They: promote the action of a neurotransmitter. interfere with or decrease the action of a neurotransmitter. replace or mimic a neurotransmitter or neuromodulator. Most drug abusers take drugs that affect dopamine and thus artificially affect this reward circuit to the point that they ignore basic physical needs in favor of the drug. Drug abusers tend to show a physiological and psychological effect. Once a person is physically dependent, they usually need more of the drug for the same effect because their body has become tolerant. Alcohol - a depressant directly absorbed from the stomach and small intestine Alcohol is the most socially accepted form of drug use. About 80% of college-aged people drink. Alcohol denatures proteins and causes damage to tissues such as the brain and liver; chronic consumption can damage the frontal lobe. High blood alcohol levels can lead to poor judgment, loss of coordination, or even coma and death. Nicotine - stimulant derived from tobacco plant Nicotine stimulates neurons to release dopamine that reinforces dependence on the drug. It adversely affects a developing embryo or fetus. Smoking increases heart rate and blood pressure. Nicotine causes psychological and physiological dependency. Cocaine - stimulant derived from a shrub Cocaine causes a rush sensation that lasts from 5-30 minutes. A cocaine binge occurs when a user takes the drug at ever-higher doses, resulting in hyperactivity, little desire for food and sleep, and an increased sex drive. There is extreme physical dependence with this drug. "Crack" is the street name for cocaine that is processed to a free-base form for smoking. Powder form is called speed and crystal form is called meth or ice. It is a stimulant that reverses the effects of fatigue and is a mood elevator. High agitation is common after the rush and can lead to violent behavior. Methamphetamine causes psychological dependency and hallucinations. "Ecstasy" is the street name for a drug that has the same effects as meth without the hallucinations. Heroin - depressant from the sap of the opium poppy plant It leads to a feeling of euphoria and no pain because it is delivered to the brain and converted into morphine. Side effects are nausea, vomiting, and depression of the respiratory and circulatory systems. Heroin use can lead to HIV, hepatitis, and other infections due to shared needles. Extreme dependency is common. Marijuana - psychoactive drug derived from a hemp plant called Cannabis It is most often smoked as a "joint." Occasional users experience mild euphoria, alterations to vision and judgment, as well as impaired motor coordination with slurred speech. Heavy users may experience depression, anxiety, hallucinations, paranoia, and psychotic symptoms. Long term use may lead to brain damage. K2 ("Spice") is a synthetic drug with higher potency than the active chemical in marijuana.
Cerebrum
Cerebral hemispheres Cerebral cortex Primary motor and sensory areas of the cortex Association areas Processing centers Central white matter Divided into four lobes Frontal lobe: primary motor area and conscious thought Temporal lobe: primary auditory, smell, and speech area Parietal lobe: primary somatosensory and taste area Occipital lobe : primary visual area largest portion of the brain
The CNS: Brain
Cerebrum Diencephalon Cerebellum Brain stem
Synaptic integration
Integration is the summation of the inhibitory and excitatory signals received by a postsynaptic neuron. This occurs because a neuron receives many signals.
The CNS: Spinal cord
It extends from the base of the brain and along the length of the vertebral canal formed by the vertebrae. The spinal cord functions to provide communication between the brain and most of the body. It is the center for reflex arcs. Gray matter in the center is a butterfly shape. White matter surrounds the gray matter.
The peripheral nervous system (PNS)
It includes cranial nerves (12 pairs), spinal nerves (31 pairs), and ganglia outside the CNS. Spinal nerves conduct impulses to and from the spinal cord. Cranial nerves conduct impulses to and from the brain. The PNS is divided into two systems. Somatic division Autonomic division
The limbic system
It joins primitive emotions (i.e., fear, pleasure) with higher functions such as reasoning. The limbic system can cause strong emotional reactions to situations but conscious thought can override and direct our behavior. Includes Amygdala - imparts emotional overtones Hippocampus - important to learning and memory
Higher mental functions
Learning - what happens when we recall and use past memories Memory - ability to hold a thought or to recall past events Short-term memory - retention of information for only a few minutes
Higher mental functions
Long-term memory - retention of information for more than a few minutes and includes the following Episodic memory - people and events Semantic memory - numbers and words Skill memory - performing skilled motor activities (i.e., riding a bike) Language - depends on semantic memory
The sarcomere
Made of 2 protein myofilaments A thick filament is composed of several hundred molecules of the protein myosin. Each myosin molecule is shaped like a golf club. Primarily, a thin filament consists of two intertwining strands of the protein actin. These filaments slide over one another during muscle contraction.
The brain stem
Midbrain - relay station between the cerebrum and spinal cord or cerebellum; reflex center Pons - a bridge between cerebellum and the CNS; regulates breathing rate; reflex center for head movements Medulla oblongata - contains reflex centers for regulating breathing, heartbeat, and blood pressure Reticular formation - major component of the reticular activating system (RAS) that regulates alertness
How does transmission across the synapse occur?
Nerve impulse reaches the axon terminal. Calcium ions enter the axon terminal and stimulate the synaptic vesicles to fuse with the presynaptic membrane. Neurotransmitters are released and diffuse across the synapse, where they bind with the postsynaptic membrane to inhibit or excite the neuron.
The beginning of muscle contraction: The sliding filament model
Nerve impulses travel down a motor neuron to a neuromuscular junction. Acetylcholine (ACh) is released from the neuron and binds to the muscle fiber. This binding stimulates the fiber causing calcium to be released from the sarcoplasmic reticulum. Released calcium combines with troponin, a molecule associated with actin. This causes the tropomyosin threads around actin to shift and expose myosin binding sites. Myosin heads bind to these sites forming cross-bridges. ATP binds to the myosin heads and is used for energy to pull the actin filaments towards the center of the sarcomere - contraction now occurs.
Cerebellum
Receives and integrates sensory input from the eyes, ears, joints, and muscles about the current position of the body Functions Maintains posture Coordinates voluntary movement Allows learning of new motor skills (i.e., playing the piano or hitting a baseball)
The nerve impulse: Resting potential (RP)
Resting potential - when the axon is not conducting a nerve impulse More positive ions outside than inside the membrane Negative charge of -70 mV inside the axon More Na+ outside than inside More K+ inside than outside
Examples of how skeletal muscles are named
Size - the gluteus maximus is the largest buttock muscle Shape - the deltoid is triangular (Greek letter delta is Δ) Location - the frontalis overlies the frontal bone Direction of muscle fiber - the rectus abdominis is longitudinal (rectus means straight)
Types of muscle tissue
Smooth - involuntary muscle found in hollow organs and vessels Cardiac - involuntary muscle found in the heart Skeletal - voluntary muscle that is attached to the skeleton
What are the functions of skeletal muscles?
Support the body by allowing us to stay upright Allow for movement by attaching to the skeleton Help maintain a constant body temperature Assist in movement in the cardiovascular and lymphatic vessels Protect internal organs and stabilize joints
The PNS: Autonomic division
Sympathetic division: coordinates the body for the "fight or flight" response by speeding up metabolism, heart rate, and breathing while slowing down and regulating other functions. Parasympathetic division: counters the sympathetic system by bringing up a relaxed state by slowing down metabolism, heart rate, and breathing, and returning other functions to normal.
How are skeletal muscles attached?
Tendon - connective tissue that connects muscle to bone Origin - attachment of a muscle on a stationary bone Insertion - attachment of a muscle on a bone that moves Antagonistic - muscles that work in opposite pairs Synergistic - muscles working in groups for a common action
Muscle fibers/cells
Terminology for cell structure The plasma membrane is called the sarcolemma. The cytoplasm is called the sarcoplasm. The SER of a muscle cell is called the sarcoplasmic reticulum and stores calcium Terminology for structure within a whole muscle Muscle fibers are arranged in bundles called fascicles. Myofibrils are bundles of myofilaments that run the length of a fiber. Myofilaments are proteins (actin and myosin) that are arranged in repeating units. Sarcomeres are the repeating units of actin and myosin found along a myofibril.
The central nervous system
The CNS consists of the brain and spinal cord. Both are protected by Bones - skull and vertebral column Meninges - 3 protective membranes that wrap around CNS Cerebral spinal fluid (CSF) - space between meninges is filled with this fluid that cushions and protects the CNS Both the brain and spinal cord are made up of two types of nervous tissue. Gray matter - contains cell bodies and nonmyelinated fibers White matter - contains myelinated axons
The PNS: Autonomic division
The autonomic system regulates the activity of involuntary muscles (cardiac and smooth) and glands.
The nervous system
The nervous system allows for communication between cells through sensory input, integration of data, and motor output. Two cell types: neurons and neuroglia
The PNS: Somatic division
The somatic system serves the skin, skeletal muscles and tendons. Automatic responses are called reflexes.
The synapse
The synapse is a small gap between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane). Transmission is accomplished across this gap by a neurotransmitter (e.g., ACh, dopamine, or serotonin). Neurotransmitters are stored in synaptic vesicles in the axon terminals.
Expanding on neurons
Three types of neurons Sensory - takes impulses from sensory receptor to CNS Interneuron - receives information in the CNS and sends it to a motor neuron Motor - takes impulses from the CNS to an effector (i.e., gland or muscle fiber) Neuron structure (Ch. 4 review) Cell body - main cell where nucleus and most organelles reside Dendrites - many short extensions that carry impulses to a cell body Axon (nerve fiber) - single, long extension that carries impulses away from the cell body
The nervous divisions
Two divisions Central nervous system (CNS): Brain and spinal cord Peripheral nervous system (PNS): Nerves and ganglia (collections of cell bodies)
Thalamus
Two masses of gray matter that receive all sensory input except smell; involved in memory and emotions
Primary somatosensory area
for sensory information from skeletal muscle and skin
Hypothalamus
helps maintain homeostasis (hunger, sleep, thirst, body temperature, and water balance) and controls pituitary gland
Association areas
integration occurs here
Processing centers
perform higher level analytical functions including Wernicke's and Broca's areas, both involved in speech
Pineal gland
secretes melatonin that controls our daily rhythms
Cerebral cortex
thin, outer layer of gray matter
Primary motor area
voluntary control of skeletal muscle
