Our responses to stimuli may be voluntary or involuntary or both Example: in response to low blood pressure, you may contract smooth muscles to decrease the diameter of your blood vessels, AND feel thirsty, causing you to take a drink
Central and peripheral nervous systems Your central nervous system (CNS) consists of your brain & spinal cord Your peripheral nervous system (PNS) consists of all the nerves that carry information to and from your CNS
Cells of the nervous system There are two main types of cells in the nervous system: Neurons: communicate with other cells using electrical and chemical signals Neuroglia: support and insulate the neurons; FAR more abundant than neurons
Parts of a neuron Cell body Dendrites: receive signals from other neurons Axons: send signals to other cells Schwann cells (neuroglial cells) wrap around the axons to form myelin
Schwann cells form myelin in the PNS Schwann cells form myelin by wrapping around PNS neurons Oligodendrocytes form myelin by wrapping around CNS neurons “White matter” is nerve tissue wrapped in myelin (axons), “gray matter” is unmyelinated (usually cell bodies)
Multiple sclerosis Autoimmune disease that attacks myelin in both the CNS & PNS Multiple functions of the nervous system may be impaired
Many types of sensory receptors In response to physical stimulation, sensory receptor cells create electrical signals that travel to the central nervous system Specialized senses (hearing, sight, smell & taste) have special receptor cells to be discussed in chapter 8
Electrical signals generated by neurons are action potentials Electrical energy is the result of movement of ions When neurons generate action potentials it involves ions moving across the cell’s plasma membrane An action potential is an electrical signal that starts in a neuron and travels down the axon
The synapse When electrical signals reach the end of axons, they trigger the release of chemicals from the axon terminal The space between the axon terminal and another cell is called the synaptic cleft and the connection between the two is called the synapse
Neurotransmitters are released at the synapse Neurotransmitters are chemical signals released from a neuron’s axon terminal onto a target cell The target cell may be a neuron, too, or another cell type Many recreational and therapeutic drugs work by influencing the action of neurotransmitters
Reflexes A reflex is an automatic response to a stimulus Reflexes can control either skeletal muscles (somatic reflexes) or involuntary muscles (autonomic reflexes) Reflexes are integrated by your spinal cord NOT your brain, hence they are not conscious actions
4 major regions of the brain Brain stem: controls breathing and blood pressure; many nerves pass through Cerebellum: controls movement Diencephalon: integrates sensory information & mediates emotional response Cerebrum: controls all “higher thought”
Areas of the cerebrum are specialized for different functions
The cerebral cortex receives sensory information and sends motor information
The CNS is vulnerable to damage Cells of the central nervous system have a very limited ability to regenerate themselves The cells themselves are soft and easily damaged (your brain has the consistency of tofu) The blood-brain barrier refers to the fact that capillaries in the brain are less permeable than those in other parts of the body; this helps protect your brain from damage due to chemicals in your bloodstream
Bones and meninges protect the CNS The meninges consist of the: – dura mater – arachnoid mater – pia mater layers of connective tissue membrane that protect the brain and spinal cord Meningitis is inflammation of the meninges caused by viral or bacterial infection; can be serious or fatal!
Cerebrospinal fluid in and around the brain and spinal cord also protects it
Hydrocephalus is caused by an overabundance of CSF
Traumatic brain injuries Most often caused by car accidents Concussion: a mild traumatic brain injury; may result in temporary loss of consciousness Intracranial hemorrhage: bleeding in the brain; can damage brain tissue Cerebral edema: swelling of the brain; sometimes part of the skull is temporarily removed to treat this
Stroke Stroke is the result of a blood clot that blocks blood flow to part of the brain; if brain tissue is deprived of blood for even a few minutes, it dies Aphasia, or reduced ability to produce or understand language, is common after stroke affecting the left hemisphere
The spinal cord Spinal nerves carry information both to and from the CNS The nerves then split and the sensory information goes in through a structure called the dorsal root; motor information goes out through the ventral root
The spinal cord Dorsal horns (gray matter) contain interneurons that connect neurons to each other White matter of the spinal cord is myelinated axons carrying info up and down
The sympathetic and parasympathetic divisions Sympathetic nervous system is activated under “fight or flight conditions” – Blood flow to muscles increases – Pupils of eyes dilate – Digestion is inhibited – Heart rate increases Parasympathetic nervous system is activated under “rest and digest” conditions Table 7.3 in your book lists several specific effects each of these has!
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