Deconstructing the Nervous System

1. Deconstructing the Nervous System • Smallest structural unit is the neuron • Do not divide and aren’t replaced when they die • Glia are cells that support the neuron by providing nourishment and insulation of the axon • More numerous than neurons • Consists of 2 main divisions

2. Nervous System Divisions

3. Reflexes • Automatic responses to stimuli, i.e knee-jerk • 5 main stages/components • Receptor • Detects stimuli • Sensory neuron • Signal towards CNS • Integration center • Spinal cord • Motor neuron • Signal exits CNS • Effector • Produces a response to stimuli

4. The Incredible Edible Neuron • Cell body • Stores the organelles, including the nucleus, and neurotransmitters • Dendrites • Receive signals and conveys information to cell body • Highly branched and often shorter (than axon) • Axon • Transmits signals to other cells • Coated in a thick insulating material called myelin sheath • Each is a Schwann cell and the spaces between are nodes of Ranvier • Only place where axon is leaky • Salutatory conduction • Multiple sclerosis (MS) immune system destroys myelin • Singular and longer • Synaptic terminal, branched end of axon that meets other cells • Forms a synapse or point of communication between cells

6. Parasympathetic Neurons from brain and lower spinal cord Synapse within target organs Sympathetic emerge from middle of spinal cord Synapse at target organs Both cooperate to maintain homeostasis Autonomic Nervous System

7. The Human Brain • Brain is protected via multiple structures • Blood brain barrier • Selective permeability • Meningial layers • Cerebrospinal fluid • Cushions CNS and provides nutrients • 3 main regions • brainstem is pons, medulla oblongata, and midbrain

8. Biological clock is regulated by the suprachiasmatic nucleus (SCN) responding to visual input to maintain circadian rhythms Maintained without external clues Cerebrum has 2 hemispheres, connected by the corpus callosum Control opposite sides of body Brain Structure Functions

9. Cerebral Cortex • Convolutions maximize neurons in limited space • Responsible for human traits • Receives stimuli from all senses • Regulates voluntary movements • 4 lobes • Frontal, (2) parietal, (2) temporal, and occipital • Each with specialized functions • Association areas where higher order processes occur, ‘thinking’

10. Decoding Lobes of the Brain • Cerebral hemispheres demonstrate lateralization • Left=objective (language and logic) • Right=subjective (creative endeavors) • Frontal lobe • Motor cortex sends signals to muscles; higher order processes • Parietal lobe • Somatosensory cortex receives and integrates stimuli from sensory systems • Temporal lobe • Memory, hearing, and language • Occipital lobe • Vision

11. Decoding Brain Structures • Cerebellum • Involved in coordination, balance, movement, posture, and planning learned movements • Brain stem • Controls heart rate, breathing, and digestion; also emesis center • Olfactory bulb • Controls smell • Optic bulb • Controls vision • Reticular formation • Alertness and attentiveness • Thalamus • Relays sensory info to cortex and multiple sensations • Hypothalamus • Controls ANS, pituitary, and regulates brainstem

12. Turkey Makes Me Sleepy • Arousal is a state of awareness while sleep is external stimuli that isn’t consciously perceived • Multiple brain areas contribute • Reticular formation receives sensory info and determines what reaches the cortex for processing • More info = more alert and aware • Can filter out repetitive stimuli • Pons and medulla promote sleep with stimulation • 5-HT may be a neurotransmitter (milk before bed or turkey = tryptophan) • Midbrain causes arousal • Sleep is ESSENTIAL for survival and is an ACTIVE state for the brain

13. Sleep Cycle

14. I Remember Learning to Cry • Limbic system controls memory, learning, and emotion • Include thalamus, hypothalmus, amygdala, and hippocampus • Attaches ‘feelings’ to basic survival mechanisms • Memory is ability to store and retrieve information from experience • Amygdala adds emotion, acts as a filter for remembering • Hippocampus helps form and recall memories • Factual and procedural memories differ • Odors or music can trigger memories

15. Diseases of the Brain • Schizophrenia • Lose the ability to distinguish reality • Strong genetic component • Treatments focus on DA, but can induce Parkinson symptoms • Depression • Major depression and bipolar disorder • Sadness that interferes with normal life and extreme mood swings • Genetic component • 5-HT imbalance so SSRI’s (Prozac, Paxil, and Soloft) prescribed • Alzheimer’s Disease • Dementia characterized by confusion and memory loss • Progressive disease that is hard to diagnose while alive • Tangles and plaques trigger neuronal death, but cause or symptom? • Parkinson’s Disease • Difficulty in initiating movement and slowness of movement • Progressive disease where age increases risk • No cure, but treatments with DA to alleviate

17. Comparative Neural Anatomy • Cnidarians are 1st phyla to evolve a nervous system • Radially symmetrical adults have symmetrical nervous systems • Control digestive cavity contractions and tentacle movement • Bilateral symmetry usually demonstrate cephalization, nervous system concentration in the head and centralization, presence of CNS and PNS • Platyhelminthes with nerve cords to control animal movements is simplest • Subsequent phyla see an increase in neuron number and segmentation

24. Membrane Potentials • Potential energy (PE) that exists as electrical charge across the neuron’s PM • Cytoplasm charge = (-) charge, extracellular fluid = (+) charge • Stored by holding opposite charges apart across the PM • Results in the resting potential (-70 mV) • Ionic differences of intra- and extracellular fluid produce electrical differences or voltage • Potassium (K+) is high inside, sodium (Na+) is high outside cell • K+ diffuses out readily through K+ channels, leaving a (-) charge inside • Na+-K+ pump maintains by moving Na+ out and K+ in • Can change with changing permeability to ions

26. Can be electrical or chemical Electrical are found in the heart and digestive system, where steady rhythms are necessary Chemical release neurotransmitters stored in synaptic vesicles into the synaptic cleft Resulting events vary amongst synapse types Synaptic Communication

27. Neurotransmitters • Small molecules that serve as chemical signals • Can be excitatory, inhibitory, or both • Depends on action at synapse and can vary in magnitude • Excite if opens Na+ channels (flow into cell) • Inhibit if open chloride (Cl-) or K+ channels (flow in or out respectively) • Cell bodies can and often do receive both at 1 time • Summation of signals produces all-or-none response

28. Types of Neurotransmitters • Acetylcholine (ACh) is excitatory and inhibitory • Contracts skeletal muscles, but relaxes cardiac • Botulinum toxin (Botox) inhibits Ach so muscles in eyes/mouth stop contracting = no wrinkles • Monoamines have multiple roles in CNS • Include epinephrine (EPI), norepinephrine (NE), serotonin (5-HT), and dopamine (DA) • Dual roles as hormones (first 3) • Amino acids • Include aspartate, glutamate, glycine, and GABA • First 2 excitatory and last 2 inhibitory • Soluble gases • Nitric oxide (NO) • Viagra promotes NO release into erectile tissue